ALSA: es18xx: 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/20191210063454.31603-42-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/es18xx.c

@@ -1781,6 +1781,7 @@ static int snd_es18xx_new_device(struct snd_card *card,
 		return -EBUSY;
 	}
 	chip->irq = irq;
+	card->sync_irq = chip->irq;
 
 	if (request_dma(dma1, "ES18xx DMA 1")) {
 		snd_es18xx_free(card);