ALSA: maestro3: Support PCM sync_stop

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

Link: https://lore.kernel.org/r/20191210063454.31603-28-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/maestro3.c

@@ -2633,6 +2633,7 @@ snd_m3_create(struct snd_card *card, struct pci_dev *pci,
 		goto free_chip;
 	}
 	chip->irq = pci->irq;
+	card->sync_irq = chip->irq;
 
 #ifdef CONFIG_PM_SLEEP
 	chip->suspend_mem =