HID: prodikeys: constify snd_rawmidi_ops structures

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

Done with the help of Coccinelle.
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-prodikeys.c

@@ -593,7 +593,7 @@ static void pcmidi_in_trigger(struct snd_rawmidi_substream *substream, int up)
 	pm->in_triggered = up;
 }
 
-static struct snd_rawmidi_ops pcmidi_in_ops = {
+static const struct snd_rawmidi_ops pcmidi_in_ops = {
 	.open = pcmidi_in_open,
 	.close = pcmidi_in_close,
 	.trigger = pcmidi_in_trigger