ASoC: mbhc-adc: Resolve bcs not enabled for us headset

BCS is not enabled for us headset as after 3sec loop
we directly switch to report headset and bcs is still disabled.
Enable bcs only after reporting valid plug to resolve issue.

Change-Id: I69bb71d20583fd2e2be921e9b657d9c44c047708
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>