ASoC: wm8994: Prevent double lock of accdet_lock mutex on wm1811

wm1811_micd_stop takes the accdet_lock mutex, and is called from two
places, one of which is already holding the accdet_lock. This obviously
causes a lock up.

This patch fixes this issue by removing the lock from wm1811_micd_stop
and ensuring that it is always locked externally.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org