ALSA: ac97: Constify snd_ac97_res_table definition

One snd_ac97_res_table definition remains forgotten without const.
Let's add it for a bit of optimization.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-46-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/ac97/ac97_patch.c

@@ -3871,7 +3871,7 @@ static int mpatch_si3036(struct snd_ac97 * ac97)
  * check_volume_resolution().
  */
 
-static struct snd_ac97_res_table lm4550_restbl[] = {
+static const struct snd_ac97_res_table lm4550_restbl[] = {
 	{ AC97_MASTER, 0x1f1f },
 	{ AC97_HEADPHONE, 0x1f1f },
 	{ AC97_MASTER_MONO, 0x001f },