hwmon: qpnp-adc-current: Fix offset channel selection

On PM8941 depending on the status of the BATFET
the reads on channel 0 for Internal RSENSE go to
channel 5 therefore the offset is performed on that
channel. This is applicable to only to PM8941 and
not on PM8026 and PM8110. Therefore apply the check
for offset channel selection based on the BATFET
status on PM8941 only.

Change-Id: I146b244c2b562664b85e804694f8d4b2aac3fa86
CRs-Fixed: 629758
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>