hwmon: qpnp-adc-current: Add temperature compensation

The IADC does not meet accuracy spec with just gain
and offset calibration. Additional compensation is
required on top of gain/offset calibration to compensate
for variations due to chip revision, manufacturer and
temperature.

Change-Id: If69ec412b05746e49e98fff761a70cd987bd6f7e
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>