ASoC: wcd-mbhc: Avoid fake headset report during headphone remove

When headphone is removed while 3 second polling is still in progress,
mbhc hs comparator result will be read as "0" and this causes reporting
a fake headset insert event to user-space followed by headphone removal.
Avoid sending this fake headset insert event to user-space by checking
for the microphone clamp bit from codec mbhc hardware.

CRs-fixed: 941089
Change-Id: I96d96dca92a6c99bbb25ab70a2706e730c28818b
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>