ALSA: au88x0: 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/pci/au88x0/au88x0_pcm.c

@@ -439,7 +439,7 @@ static snd_pcm_uframes_t snd_vortex_pcm_pointer(struct snd_pcm_substream *substr
 }
 
 /* operators */
-static struct snd_pcm_ops snd_vortex_playback_ops = {
+static const struct snd_pcm_ops snd_vortex_playback_ops = {
 	.open = snd_vortex_pcm_open,
 	.close = snd_vortex_pcm_close,
 	.ioctl = snd_pcm_lib_ioctl,