ALSA: ac97: Treat snd_ac97_bus_ops as const

This is a preliminary patch to allow const for snd_ac97_bus_ops
definitions in each driver's code.  The ops reference is read-only,
hence it can be declared as const for further optimization.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-23-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/ac97_bus.c b/sound/ac97_bus.c
index 3732a63..b4685c5 100644
--- a/sound/ac97_bus.c
+++ b/sound/ac97_bus.c
@@ -55,7 +55,7 @@ static bool snd_ac97_check_id(struct snd_ac97 *ac97, unsigned int id,
 int snd_ac97_reset(struct snd_ac97 *ac97, bool try_warm, unsigned int id,
 	unsigned int id_mask)
 {
-	struct snd_ac97_bus_ops *ops = ac97->bus->ops;
+	const struct snd_ac97_bus_ops *ops = ac97->bus->ops;
 
 	if (try_warm && ops->warm_reset) {
 		ops->warm_reset(ac97);