ath10k: fix hwmon temperature input units

To be compliant with the hwmon interface the unit needs to be
millidegree Celsius. Fix that.

Reported-by: Matthias Kaehlcke <mka@google.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>