ALSA: midi: constify snd_rawmidi_global_ops structures

The snd_rawmidi_global_ops structures are never modified, so declare them
as const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_virmidi.c

@@ -468,7 +468,7 @@ static int snd_virmidi_dev_unregister(struct snd_rawmidi *rmidi)
 /*
  *
  */
-static struct snd_rawmidi_global_ops snd_virmidi_global_ops = {
+static const struct snd_rawmidi_global_ops snd_virmidi_global_ops = {
 	.dev_register = snd_virmidi_dev_register,
 	.dev_unregister = snd_virmidi_dev_unregister,
 };