ALSA: seq: Mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Notice that in this particular case, I replaced the code comment with
a proper "fall through" annotation, which is what GCC is expecting
to find.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_midi_emul.c

@@ -318,7 +318,7 @@ do_control(struct snd_midi_op *ops, void *drv, struct snd_midi_channel_set *chse
 		break;
 	case MIDI_CTL_MSB_DATA_ENTRY:
 		chan->control[MIDI_CTL_LSB_DATA_ENTRY] = 0;
-		/* go through here */
+		/* fall through */
 	case MIDI_CTL_LSB_DATA_ENTRY:
 		if (chan->param_type == SNDRV_MIDI_PARAM_TYPE_REGISTERED)
 			rpn(ops, drv, chan, chset);