ASoC: wcd-mbhc: Use micbias for accessory detection

Currently micbias pull-up is used for headset accessory
detection. However this would cause failures in detection
during some scenarios of slow insertion of the plug. Use
micbias instead, to detect accessory type.

Change-Id: If15c7676aa2e46b0718fbea8938cc4f2cca0948d
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>