hwmon: qpnp-adc-voltage: Add scale_type checks

Add checks for potential out of bound array overflow
for scale_type index used for reverse scaling.

Change-Id: I73a28505b7f7145790f3e2ad0e9f1781d54a3019
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>