[ALSA] remove redundent assignment to the ac97 device structure

AC97 Codec
Don't use dev.platform_data to store a reference to the containing
ac97_t structure.  Such assignment is redundent since we can deduce the
ac97_t structure location from the contained device structure.  This
sets platform_data free for other purposes.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/ac97_codec.h

@@ -527,6 +527,8 @@ struct _snd_ac97 {
 	struct device dev;
 };
 
+#define to_ac97_t(d) container_of(d, struct _snd_ac97, dev)
+
 /* conditions */
 static inline int ac97_is_audio(ac97_t * ac97)
 {

sound/pci/ac97/ac97_codec.c

@@ -1828,7 +1828,6 @@ static int snd_ac97_dev_register(snd_device_t *device)
 
 	ac97->dev.bus = &ac97_bus_type;
 	ac97->dev.parent = ac97->bus->card->dev;
-	ac97->dev.platform_data = ac97;
 	ac97->dev.release = ac97_device_release;
 	snprintf(ac97->dev.bus_id, BUS_ID_SIZE, "card%d-%d", ac97->bus->card->number, ac97->num);
 	if ((err = device_register(&ac97->dev)) < 0) {