hwmon: qpnp-adc-current: Fix setting external rsense

The iadc compensation uses the external/internal rsense
as one of the parameters for compensating the values
for current. Currently it defaults to internal rsense.
Fix this by updating the compensation rsense parameter
based on the inputs from the DT whether its internal
or external rsense.

Change-Id: Id931e20915967f410b16174eb2484377fbc858f3
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>