ALSA: ac97: Constify snd_ac97_bus_ops definitions

Now snd_ac97_bus() takes the const ops pointer, so we can define the
snd_ac97_bus_ops locally as const as well for further optimization.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-24-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/ac97/snd_ac97_compat.c

@@ -53,7 +53,7 @@ static unsigned short compat_ac97_read(struct snd_ac97 *ac97,
 	return actrl->ops->read(actrl, ac97->num, reg);
 }
 
-static struct snd_ac97_bus_ops compat_snd_ac97_bus_ops = {
+static const struct snd_ac97_bus_ops compat_snd_ac97_bus_ops = {
 	.reset = compat_ac97_reset,
 	.warm_reset = compat_ac97_warm_reset,
 	.write = compat_ac97_write,