ASoC: dapm: Add a helper to get the CODEC for DAPM kcontrol

We use the same 3 lines to get the CODEC for a kcontrol in a quite a few places.
This patch puts them into a common helper function. Having this encapsulated in
a helper function will also make it more easier to eventually change the data
layout of the kcontrol's private data.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/sound/soc/codecs/wm8995.c b/sound/soc/codecs/wm8995.c
index 90a65c4..da2899e6 100644
--- a/sound/soc/codecs/wm8995.c
+++ b/sound/soc/codecs/wm8995.c
@@ -549,12 +549,9 @@
 static int wm8995_put_class_w(struct snd_kcontrol *kcontrol,
 			      struct snd_ctl_elem_value *ucontrol)
 {
-	struct snd_soc_dapm_widget_list *wlist = snd_kcontrol_chip(kcontrol);
-	struct snd_soc_dapm_widget *w = wlist->widgets[0];
-	struct snd_soc_codec *codec;
+	struct snd_soc_codec *codec = snd_soc_dapm_kcontrol_codec(kcontrol);
 	int ret;
 
-	codec = w->codec;
 	ret = snd_soc_dapm_put_volsw(kcontrol, ucontrol);
 	wm8995_update_class_w(codec);
 	return ret;