ASoC: ams-delta: Update locking around use of DAPM pin API

The pin updates in this driver look like they are intended to be done
atomically, update to do so. It looks like these were originally locked
with the CODEC mutex and not updated since the patch "ASoC: dapm: Use
DAPM mutex for DAPM ops instead of codec mutex", so remove the original
CODEC mutex locking as well.

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