ALSA: spi: 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/20200103081714.9560-19-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/spi/at73c213.c

@@ -874,7 +874,7 @@ static int snd_at73c213_dev_free(struct snd_device *device)
 static int snd_at73c213_dev_init(struct snd_card *card,
 				 struct spi_device *spi)
 {
-	static struct snd_device_ops ops = {
+	static const struct snd_device_ops ops = {
 		.dev_free	= snd_at73c213_dev_free,
 	};
 	struct snd_at73c213 *chip = get_chip(card);