ALSA: seq: Constify struct snd_midi_op

Change the argument of snd_midi_process_event() to receive a const
snd_midi_op pointer and its callers respectively.  This allows further
optimizations.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-30-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/include/sound/seq_midi_emul.h b/include/sound/seq_midi_emul.h
index d6b7405..88799d1 100644
--- a/include/sound/seq_midi_emul.h
+++ b/include/sound/seq_midi_emul.h
@@ -174,7 +174,8 @@ enum {
 };
 
 /* Prototypes for midi_process.c */
-void snd_midi_process_event(struct snd_midi_op *ops, struct snd_seq_event *ev,
+void snd_midi_process_event(const struct snd_midi_op *ops,
+			    struct snd_seq_event *ev,
 			    struct snd_midi_channel_set *chanset);
 void snd_midi_channel_set_clear(struct snd_midi_channel_set *chset);
 struct snd_midi_channel_set *snd_midi_channel_alloc_set(int n);