ASoC: Constify pin names for DAPM pin status APIs

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/include/sound/soc-dapm.h b/include/sound/soc-dapm.h
index cc99dd4..075244e 100644
--- a/include/sound/soc-dapm.h
+++ b/include/sound/soc-dapm.h
@@ -260,10 +260,10 @@
 int snd_soc_dapm_sys_add(struct device *dev);
 
 /* dapm audio pin control and status */
-int snd_soc_dapm_enable_pin(struct snd_soc_codec *codec, char *pin);
-int snd_soc_dapm_disable_pin(struct snd_soc_codec *codec, char *pin);
-int snd_soc_dapm_nc_pin(struct snd_soc_codec *codec, char *pin);
-int snd_soc_dapm_get_pin_status(struct snd_soc_codec *codec, char *pin);
+int snd_soc_dapm_enable_pin(struct snd_soc_codec *codec, const char *pin);
+int snd_soc_dapm_disable_pin(struct snd_soc_codec *codec, const char *pin);
+int snd_soc_dapm_nc_pin(struct snd_soc_codec *codec, const char *pin);
+int snd_soc_dapm_get_pin_status(struct snd_soc_codec *codec, const char *pin);
 int snd_soc_dapm_sync(struct snd_soc_codec *codec);
 
 /* dapm widget types */