ALSA: vxpocket: Support PCM sync_stop

The driver invokes snd_pcm_period_elapsed() simply from the threaded
interrupt handler.  Set card->sync_irq for enabling the missing
sync_stop PCM operation.

Link: https://lore.kernel.org/r/20191210063454.31603-55-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pcmcia/vx/vxpocket.c

@@ -185,6 +185,7 @@ static int snd_vxpocket_assign_resources(struct vx_core *chip, int port, int irq
 		card->shortname, port, irq);
 
 	chip->irq = irq;
+	card->sync_irq = chip->irq;
 
 	if ((err = snd_vx_setup_firmware(chip)) < 0)
 		return err;