ALSA: usb: constify snd_pcm_ops structures

snd_pcm_ops are not supposed to change at runtime. All functions
working with snd_pcm_ops provided by <sound/pcm.h> work with
const snd_pcm_ops. So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/pcm.c

@@ -1690,7 +1690,7 @@ static int snd_usb_substream_capture_trigger(struct snd_pcm_substream *substream
 	return -EINVAL;
 }
 
-static struct snd_pcm_ops snd_usb_playback_ops = {
+static const struct snd_pcm_ops snd_usb_playback_ops = {
 	.open =		snd_usb_playback_open,
 	.close =	snd_usb_playback_close,
 	.ioctl =	snd_pcm_lib_ioctl,
@@ -1703,7 +1703,7 @@ static struct snd_pcm_ops snd_usb_playback_ops = {
 	.mmap =		snd_pcm_lib_mmap_vmalloc,
 };
 
-static struct snd_pcm_ops snd_usb_capture_ops = {
+static const struct snd_pcm_ops snd_usb_capture_ops = {
 	.open =		snd_usb_capture_open,
 	.close =	snd_usb_capture_close,
 	.ioctl =	snd_pcm_lib_ioctl,