iio: accel: bmc150: Remove bmc150_set/get_second_device() accessor functions

Now that the definition of the bmc150_accel_data struct is no longer
private to bmc150-accel-core.c, bmc150-accel-i2c.c can simply directly
access the second_dev member and the accessor functions are no longer
necessary.

Note if the i2c_acpi_new_device() for the second-client now fails,
an ERR_PTR gets stored in data->second_dev this is fine since it is only
ever passed to i2c_unregister_device() which has an IS_ERR_OR_NULL() check.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210523170103.176958-7-hdegoede@redhat.com


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