iio: imu: inv_mpu6050: Drop use of %hhx format string.

Since:
commit cbacb5ab ("docs: printk-formats: Stop encouraging use of
unnecessary %h[xudi] and %hh[xudi]")
use of these format strings has been discouraged.

Use the 0x02x form as the length specifier when used with # includes
the 0x prefix and is very unlikely to be what was intended by the author.

Part of a series removing all uses from IIO in the interestings of
avoiding providing bad examples for people to copy.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20210603180612.3635250-4-jic23@kernel.org