iio: imu: inv_mpu6050: fix temperature reporting using bad unit

Temperature should be reported in milli-degrees, not degrees. Fix
scale and offset values to use the correct unit.

This is a fix for an issue that has been present for a long time.
The fixes tag reflects the point at which the code last changed in a
fashion that would make this fix patch no longer apply.  Backports
will be necessary to fix those elements that predate that patch.

Fixes: 1615fe41 ("iio: imu: mpu6050: Fix FIFO layout for ICM20602")
Cc: stable@vger.kernel.org
Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>