iio: imu: inv_mpu6050: refactor aux read/write to use shared xfer logic

iio: imu: inv_mpu6050: refactor aux read/write to use shared xfer logic

Refactors inv_mpu_aux_read() and inv_mpu_aux_write() to extract the common
I2C transfer sequence into inv_mpu_i2c_master_xfer(), which now handles
starting and stopping the I2C master, waiting for completion, disabling
SLV0, and checking for NACK errors.

This refactoring removes code duplication and improves maintainability.
No functional changes are intended.

Signed-off-by: Isabella Caselli <bellacaselli20@gmail.com>
Co-developed-by: Rodrigo Michelassi <rodrigo.michelassi@usp.br>
Signed-off-by: Rodrigo Michelassi <rodrigo.michelassi@usp.br>
Acked-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
Link: https://patch.msgid.link/20250507184539.54658-1-bellacaselli20@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>