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>
diff --git a/sound/usb/caiaq/audio.c b/sound/usb/caiaq/audio.c
index 054645f..fb1c1ea 100644
--- a/sound/usb/caiaq/audio.c
+++ b/sound/usb/caiaq/audio.c
@@ -338,7 +338,7 @@ snd_usb_caiaq_pcm_pointer(struct snd_pcm_substream *sub)
 }
 
 /* operators for both playback and capture */
-static struct snd_pcm_ops snd_usb_caiaq_ops = {
+static const struct snd_pcm_ops snd_usb_caiaq_ops = {
 	.open =		snd_usb_caiaq_substream_open,
 	.close =	snd_usb_caiaq_substream_close,
 	.ioctl =	snd_pcm_lib_ioctl,