iio:measurement specialties core: Fix endian sparse warnings.

This patch changes various types to the appropriate endian specific
versions.  Also introduces an additional local variable to avoid
a single variable being used for both be and cpu endianness.

These aren't bugs as such, but clearing them up does make the code
clearer.

Warning was:
sparse warnings: (new ones prefixed by >>)

>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:126:9: sparse: cast to restricted __be32
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:126:9: sparse: cast to restricted __be32
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:126:9: sparse: cast to restricted __be32
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:126:9: sparse: cast to restricted __be32
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:126:9: sparse: cast to restricted __be32
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:126:9: sparse: cast to restricted __be32
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:127:16: sparse: cast to restricted __be32
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:127:16: sparse: cast to restricted __be32
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:127:16: sparse: cast to restricted __be32
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:127:16: sparse: cast to restricted __be32
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:127:16: sparse: cast to restricted __be32
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:127:16: sparse: cast to restricted __be32
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:208:18: sparse: incorrect type in assignment (different base types)
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:208:18:    expected unsigned short [unsigned] [addressable] [usertype] send_buf
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:208:18:    got restricted __be16 [usertype] <noident>
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
>> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:216:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:230:18: sparse: incorrect type in assignment (different base types)
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:230:18:    expected unsigned short [unsigned] [addressable] [usertype] send_buf
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:230:18:    got restricted __be16 [usertype] <noident>
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64
   drivers/iio/common/ms_sensors/ms_sensors_i2c.c:239:19: sparse: cast to restricted __be64

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>