hwmon: qpnp-adc-common: Update scaling api names

Update api name used for converting voltage-temperature
and temperature-voltage from the mapping table to make
it more obvious for clients to call the appropriate
functions.

Change-Id: I582f9dabd563a3c8cf0a9b580adb1a355856099a
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>