hwmon: qpnp-adc-voltage: Add version check for case_therm channel

case_therm channel is used for reading the skin temperature.
Calibration type for above thermistor channel has to be absolute
for PM8950 1.0 and ratiometric for PM8950 2.0. Add version check to
detect the PMIC used and update the calibration type accordingly.

Change-Id: Ia9e959ca496cbbb9131a4786cc1c79402bf2b005
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>