hwmon: qpnp-adc-voltage: Update VADC settings mask

Update the mask to use default settings to enable fast
average for channel configuration. Setting this allows
low latency for multiple averaged conversions. Also
update the field mask for hardware settling delay.

Change-Id: If50943f86a6d3f54039a0b4ed4f8a71c8aaaa1fa
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>