ALSA: drivers: Constify snd_rawmidi_ops

Now snd_rawmidi_ops is maintained as a const pointer in snd_rawmidi,
we can constify the definitions.

Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/mtpav.c

@@ -600,13 +600,13 @@ static int snd_mtpav_get_ISA(struct mtpav *mcard)
 /*
  */
 
-static struct snd_rawmidi_ops snd_mtpav_output = {
+static const struct snd_rawmidi_ops snd_mtpav_output = {
 	.open =		snd_mtpav_output_open,
 	.close =	snd_mtpav_output_close,
 	.trigger =	snd_mtpav_output_trigger,
 };
 
-static struct snd_rawmidi_ops snd_mtpav_input = {
+static const struct snd_rawmidi_ops snd_mtpav_input = {
 	.open =		snd_mtpav_input_open,
 	.close =	snd_mtpav_input_close,
 	.trigger =	snd_mtpav_input_trigger,