ASoC: wcd-mbhc: initialize boolean flag anc_mic_found

As anc_mic_found is not initialized, it is taking
input as true and report as ANC Headphone results
in wrong accessory detection. Initialize the flag
to false that fixes the issue.

Change-Id: I1c9912e2ab396a8a0a31065b826d6f92a0603215
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>