usb: gadget: f_midi: constify snd_rawmidi_ops structures

These snd_rawmidi_ops structures are only passed as the third
argument of snd_rawmidi_set_ops.  This argument is const, so the
snd_rawmidi_ops structures can be const too.

Done with the help of Coccinelle.
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/function/f_midi.c

@@ -755,13 +755,13 @@ static void f_midi_out_trigger(struct snd_rawmidi_substream *substream, int up)
 		clear_bit(substream->number, &midi->out_triggered);
 }
 
-static struct snd_rawmidi_ops gmidi_in_ops = {
+static const struct snd_rawmidi_ops gmidi_in_ops = {
 	.open = f_midi_in_open,
 	.close = f_midi_in_close,
 	.trigger = f_midi_in_trigger,
 };
 
-static struct snd_rawmidi_ops gmidi_out_ops = {
+static const struct snd_rawmidi_ops gmidi_out_ops = {
 	.open = f_midi_out_open,
 	.close = f_midi_out_close,
 	.trigger = f_midi_out_trigger