ALSA: line6: Don't handle PCM trigger for other cards

Otherwise it oopses.
Tested-by: NChris Rorvick <chris@rorvick.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/usb/line6/pcm.c

@@ -233,6 +233,8 @@ int snd_line6_trigger(struct snd_pcm_substream *substream, int cmd)
 	clear_bit(LINE6_INDEX_PREPARED, &line6pcm->flags);
 
 	snd_pcm_group_for_each_entry(s, substream) {
+		if (s->pcm->card != substream->pcm->card)
+			continue;
 		switch (s->stream) {
 		case SNDRV_PCM_STREAM_PLAYBACK:
 			err = snd_line6_playback_trigger(line6pcm, cmd);