ASoC: wcd: acquire lock during mbhc initialise

If target is booted with headset connected, sometimes
plug type detection is happening without mbhc initialisation.
This results in improper detection of headset.
Acquire lock in mbhc initialise to stop detection routine.

Change-Id: I82f3dbcf7051ec89e984296130454c4d9e1cc696
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>