iio: imu: mpu6050: add level shifter flag

Some boards fail in magnetometer probe if level shifter flag is not set,
definition was found in the vendor Linux kernel v3.0.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
Link: https://lore.kernel.org/r/20230927173245.2151083-3-andreas@kemnade.info


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