iio: imu: inv_mpu6050: Use upper_16_bits()/lower_16_bits() helpers

Use upper_16_bits()/lower_16_bits() helpers instead of open-coding them.
This is easier to scan quickly compared to bitwise manipulation, and
it is pleasingly symmetric.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
Link: https://patch.msgid.link/20240904184543.1219866-1-andy.shevchenko@gmail.com


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