ALSA: sh: Constify snd_device_ops definitions

Now we may declare const for snd_device_ops definitions, so let's do
it for optimization.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-18-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/sh/sh_dac_audio.c

@@ -325,7 +325,7 @@ static int snd_sh_dac_create(struct snd_card *card,
 	struct snd_sh_dac *chip;
 	int err;
 
-	static struct snd_device_ops ops = {
+	static const struct snd_device_ops ops = {
 		   .dev_free = snd_sh_dac_dev_free,
 	};