hwmon: qpnp-adc-current: Fix IADC RSENSE trim error

This is a workaround for a RSENSE trim issue that may
affect some of the parts. The RSENSE might be trimmed to a
incorrect value resulting in an incorrect current value.
The workaround will check if the trim values stored in the
registers are valid and if not use a default RSENSE value.

CRs-Fixed: 606553
Change-Id: I8d77a2c6c28e57f2e537d1c5b65d0e08d5fabd90
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>