ASoC: wcd-mbhc: Avoid fake microphone insert/removal events

If headphones is removed during 3-sec polling interval,
it is possible that hs_comp_result is zero while mechanical
switch level will be low. Currently driver reports microphone
insertion followed immediately by removal in this scenario.
These fake events cause audio to continue to play on speaker
even headphones is removed during playback.

Change-Id: Ibf559e207b3370cb2cec5149f8e794cb55ca27ac
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>