ALSA: pci: 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/20200103081714.9560-28-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/es1968.c

@@ -2007,7 +2007,7 @@ snd_es1968_mixer(struct es1968 *chip)
 	struct snd_ctl_elem_id elem_id;
 #endif
 	int err;
-	static struct snd_ac97_bus_ops ops = {
+	static const struct snd_ac97_bus_ops ops = {
 		.write = snd_es1968_ac97_write,
 		.read = snd_es1968_ac97_read,
 	};