ALSA: lx6464es: Support PCM sync_stop

The driver invokes snd_pcm_period_elapsed() simply from the threaded
interrupt handler.  Set card->sync_irq for enabling the missing
sync_stop PCM operation.

Link: https://lore.kernel.org/r/20191210063454.31603-50-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/lx6464es/lx6464es.c

@@ -1002,6 +1002,7 @@ static int snd_lx6464es_create(struct snd_card *card,
 		goto request_irq_failed;
 	}
 	chip->irq = pci->irq;
+	card->sync_irq = chip->irq;
 
 	err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
 	if (err < 0)