ASoC: wcd-mbhc: Disable moisture detect threshold if duty cycle disabled

Moisture detection is not disabled properly if threshold
remains set as 24k even if duty cycle is disabled.
This is leading into headset not getting detected
sometimes. Disable threshold as well if duty cycle disabled.

Change-Id: Ic90c65d8bbaa965cf147f95edf5add8980889e1f
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>