ALSA: pci: 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>
diff --git a/sound/pci/cs4281.c b/sound/pci/cs4281.c
index 8f0f5f2..fa7c516 100644
--- a/sound/pci/cs4281.c
+++ b/sound/pci/cs4281.c
@@ -1767,14 +1767,14 @@ static void snd_cs4281_midi_output_trigger(struct snd_rawmidi_substream *substre
 	spin_unlock_irqrestore(&chip->reg_lock, flags);
 }
 
-static struct snd_rawmidi_ops snd_cs4281_midi_output =
+static const struct snd_rawmidi_ops snd_cs4281_midi_output =
 {
 	.open =		snd_cs4281_midi_output_open,
 	.close =	snd_cs4281_midi_output_close,
 	.trigger =	snd_cs4281_midi_output_trigger,
 };
 
-static struct snd_rawmidi_ops snd_cs4281_midi_input =
+static const struct snd_rawmidi_ops snd_cs4281_midi_input =
 {
 	.open = 	snd_cs4281_midi_input_open,
 	.close =	snd_cs4281_midi_input_close,