ASoC: ams-delta: Fix compile error

snd_soc_dapm_mutex_unlock() wants a pointer to the DAPM context, not the CODEC.

Fixes: 03510ca0

 ("ASoC: ams-delta: Update locking around use of DAPM pin API")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>