ASoC: Remove redundant codec pointer from DAIs

The DAI structure has two pointers to the codec, one in the body of the
DAI and one in a union for a parent pointer.  Drop the parent pointer
version.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

include/sound/soc-dai.h

@@ -205,11 +205,8 @@ struct snd_soc_dai {
 	/* DAI private data */
 	void *private_data;
 
-	/* parent codec/platform */
-	union {
-		struct snd_soc_codec *codec;
-		struct snd_soc_platform *platform;
-	};
+	/* parent platform */
+	struct snd_soc_platform *platform;
 
 	struct list_head list;
 };