ALSA: sb: 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/20191210063454.31603-47-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/sb/sb_common.c

@@ -233,6 +233,7 @@ int snd_sbdsp_create(struct snd_card *card,
 		return -EBUSY;
 	}
 	chip->irq = irq;
+	card->sync_irq = chip->irq;
 
 	if (hardware == SB_HW_ALS4000)
 		goto __skip_allocation;