ALSA: spi: 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/spi/at73c213.c

@@ -322,7 +322,7 @@ snd_at73c213_pcm_pointer(struct snd_pcm_substream *substream)
 	return pos;
 }
 
-static struct snd_pcm_ops at73c213_playback_ops = {
+static const struct snd_pcm_ops at73c213_playback_ops = {
 	.open		= snd_at73c213_pcm_open,
 	.close		= snd_at73c213_pcm_close,
 	.ioctl		= snd_pcm_lib_ioctl,