ASoC: Declare const properly for enum texts

The enum texts are supposed to be const char * const [].  Without the
second const, it gets compile warnings like
    sound/soc/codecs/max98095.c:607:2: warning: initialization discards qualifiers from pointer target type
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/soc.h

@@ -820,7 +820,7 @@ struct soc_enum {
 	unsigned char shift_r;
 	unsigned int max;
 	unsigned int mask;
-	const char **texts;
+	const char * const *texts;
 	const unsigned int *values;
 	void *dapm;
 };