ALSA: au88x0: 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/20191210063454.31603-6-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/au88x0/au88x0.c

@@ -202,6 +202,7 @@ snd_vortex_create(struct snd_card *card, struct pci_dev *pci, vortex_t ** rchip)
 		goto irq_out;
 	}
 	chip->irq = pci->irq;
+	card->sync_irq = chip->irq;
 
 	pci_set_master(pci);
 	// End of PCI setup.