ALSA: vx222: 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/20191210063454.31603-53-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/vx222/vx222.c

@@ -163,6 +163,7 @@ static int snd_vx222_create(struct snd_card *card, struct pci_dev *pci,
 		return -EBUSY;
 	}
 	chip->irq = pci->irq;
+	card->sync_irq = chip->irq;
 
 	if ((err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops)) < 0) {
 		snd_vx222_free(chip);