ASoC: dapm: Support second register for DAPM control updates

To support double channel shared controls split across 2 registers, one
for each channel, we must be able to update both registers together.

Add a second set of register fields to struct snd_soc_dapm_update, and
update the DAPM control writeback (put) callbacks to support this.

For codecs that use custom events which call into DAPM to do updates,
also clear struct snd_soc_dapm_update before using it, so the second
set of fields remains clean.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm9712.c

@@ -187,7 +187,7 @@ static int wm9712_hp_mixer_put(struct snd_kcontrol *kcontrol,
 	struct soc_mixer_control *mc =
 		(struct soc_mixer_control *)kcontrol->private_value;
 	unsigned int mixer, mask, shift, old;
-	struct snd_soc_dapm_update update;
+	struct snd_soc_dapm_update update = { 0 };
 	bool change;
 
 	mixer = mc->shift >> 8;