ALSA: gus: 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/20191210063454.31603-43-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/gus/gus_main.c

@@ -181,6 +181,7 @@ int snd_gus_create(struct snd_card *card,
 		return -EBUSY;
 	}
 	gus->gf1.irq = irq;
+	card->sync_irq = irq;
 	if (request_dma(dma1, "GUS - 1")) {
 		snd_printk(KERN_ERR "gus: can't grab DMA1 %d\n", dma1);
 		snd_gus_free(gus);

sound/isa/gus/gusmax.c

@@ -282,7 +282,8 @@ static int snd_gusmax_probe(struct device *pdev, unsigned int dev)
 		goto _err;
 	}
 	maxcard->irq = xirq;
-	
+	card->sync_irq = maxcard->irq;
+
 	err = snd_wss_create(card,
 			     gus->gf1.port + 0x10c, -1, xirq,
 			     xdma2 < 0 ? xdma1 : xdma2, xdma1,

sound/isa/gus/interwave.c

@@ -667,6 +667,7 @@ static int snd_interwave_probe(struct snd_card *card, int dev)
 		return -EBUSY;
 	}
 	iwcard->irq = xirq;
+	card->sync_irq = iwcard->irq;
 
 	err = snd_wss_create(card,
 			     gus->gf1.port + 0x10c, -1, xirq,