ALSA: es1688: 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/20191210063454.31603-41-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/es1688/es1688_lib.c

@@ -638,6 +638,7 @@ int snd_es1688_create(struct snd_card *card,
 	}
 
 	chip->irq = irq;
+	card->sync_irq = chip->irq;
 	err = request_dma(dma8, "ES1688");
 
 	if (err < 0) {