ALSA: ump: Fix the discard error code from snd_ump_legacy_open()

snd_ump_legacy_open() didn't return the error code properly even if it
couldn't open.  Fix it.

Fixes: 0b5288f5 ("ALSA: ump: Add legacy raw MIDI support")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20240220150843.28630-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/ump.c

@@ -985,7 +985,7 @@ static int snd_ump_legacy_open(struct snd_rawmidi_substream *substream)
 	struct snd_ump_endpoint *ump = substream->rmidi->private_data;
 	int dir = substream->stream;
 	int group = ump->legacy_mapping[substream->number];
-	int err;
+	int err = 0;
 
 	mutex_lock(&ump->open_mutex);
 	if (ump->legacy_substreams[dir][group]) {
@@ -1009,7 +1009,7 @@ static int snd_ump_legacy_open(struct snd_rawmidi_substream *substream)
 	spin_unlock_irq(&ump->legacy_locks[dir]);
  unlock:
 	mutex_unlock(&ump->open_mutex);
-	return 0;
+	return err;
 }
 
 static int snd_ump_legacy_close(struct snd_rawmidi_substream *substream)