iio: imu: inv_mpu6050: Fix multiline comments style

The preffered style for long (multi-line) comments is:

/*
 * this is a multiline
 * comment
 */

This also fixes checkpatch.pl warning:
WARNING: Block comments use * on subsequent lines

Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>