hwmon: qpnp-current: Fix parameter configuration for IADC

Removing redundant parameters which are not applicable
on the IADC peripheral.

Fix the issue with "fast_avg_setup" and "decimation"
parameters to configure correctly as per channel
configuration.

Change-Id: Idfe823effc6255b57e31f37621971aab29f08020
Signed-off-by: Dipen Parmar <dipenp@codeaurora.org>