ASoC: Fix prefixing of DAPM controls by factoring prefix into snd_soc_cnew()

Currently will ignore prefixes when creating DAPM controls. Since currently
all control creation goes through snd_soc_cnew() we can fix this by factoring
the prefixing into that function.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>
diff --git a/include/sound/soc.h b/include/sound/soc.h
index 14f601f..bfa4836 100644
--- a/include/sound/soc.h
+++ b/include/sound/soc.h
@@ -340,7 +340,8 @@
  *Controls
  */
 struct snd_kcontrol *snd_soc_cnew(const struct snd_kcontrol_new *_template,
-	void *data, char *long_name);
+				  void *data, char *long_name,
+				  const char *prefix);
 int snd_soc_add_controls(struct snd_soc_codec *codec,
 	const struct snd_kcontrol_new *controls, int num_controls);
 int snd_soc_info_enum_double(struct snd_kcontrol *kcontrol,