ALSA: dummy: Constify snd_pcm_ops definitions

The snd_pcm_ops items defined in snd-dummy driver can be gracefully
declared as const.  Let's mark them for further optimization.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-44-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/dummy.c

@@ -644,7 +644,7 @@ static struct page *dummy_pcm_page(struct snd_pcm_substream *substream,
 	return virt_to_page(dummy_page[substream->stream]); /* the same page */
 }
 
-static struct snd_pcm_ops dummy_pcm_ops = {
+static const struct snd_pcm_ops dummy_pcm_ops = {
 	.open =		dummy_pcm_open,
 	.close =	dummy_pcm_close,
 	.hw_params =	dummy_pcm_hw_params,
@@ -653,7 +653,7 @@ static struct snd_pcm_ops dummy_pcm_ops = {
 	.pointer =	dummy_pcm_pointer,
 };
 
-static struct snd_pcm_ops dummy_pcm_ops_no_buf = {
+static const struct snd_pcm_ops dummy_pcm_ops_no_buf = {
 	.open =		dummy_pcm_open,
 	.close =	dummy_pcm_close,
 	.hw_params =	dummy_pcm_hw_params,
@@ -670,7 +670,7 @@ static int snd_card_dummy_pcm(struct snd_dummy *dummy, int device,
 			      int substreams)
 {
 	struct snd_pcm *pcm;
-	struct snd_pcm_ops *ops;
+	const struct snd_pcm_ops *ops;
 	int err;
 
 	err = snd_pcm_new(dummy->card, "Dummy PCM", device,