ASoC: dapm: Constify lots of names that are never modified

Neater and avoids warnings when used in other places where const strings
are desired.

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 8fa4dca..1e16d6e 100644
--- a/include/sound/soc.h
+++ b/include/sound/soc.h
@@ -366,7 +366,7 @@
  *Controls
  */
 struct snd_kcontrol *snd_soc_cnew(const struct snd_kcontrol_new *_template,
-				  void *data, char *long_name,
+				  void *data, const char *long_name,
 				  const char *prefix);
 int snd_soc_add_codec_controls(struct snd_soc_codec *codec,
 	const struct snd_kcontrol_new *controls, int num_controls);