ALSA: opl3sa2: 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/20191210063454.31603-45-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/opl3sa2.c

@@ -659,6 +659,7 @@ static int snd_opl3sa2_probe(struct snd_card *card, int dev)
 		return -ENODEV;
 	}
 	chip->irq = xirq;
+	card->sync_irq = chip->irq;
 	err = snd_wss_create(card,
 			     wss_port[dev] + 4, -1,
 			     xirq, xdma1, xdma2,