iio: accel: mma9551_core: Prevent uninitialized variable in mma9551_read_config_word()

Smatch Warns:
drivers/iio/accel/mma9551_core.c:299
	mma9551_read_config_word() error: uninitialized symbol 'v'.

When (offset >= 1 << 12) is true mma9551_transfer() will return -EINVAL
without 'v' being initialized, so check for the error and return.

Note: No actual bug as caller checks the return value and does not
use the parameter in the problem case.

Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Link: https://lore.kernel.org/r/20230126153610.3586243-1-harshit.m.mogalapalli@oracle.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>