ALSA: echoaudio: 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.  It's cleared and reset dynamically at IRQ re-acquiring for
the PM resume, too.

Link: https://lore.kernel.org/r/20191210063454.31603-16-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/echoaudio/echoaudio.c

@@ -1928,6 +1928,7 @@ static int snd_echo_create(struct snd_card *card,
 		return -EBUSY;
 	}
 	chip->irq = pci->irq;
+	card->sync_irq = chip->irq;
 	dev_dbg(card->dev, "pci=%p irq=%d subdev=%04x Init hardware...\n",
 		chip->pci, chip->irq, chip->pci->subsystem_device);
 
@@ -2151,6 +2152,7 @@ static int snd_echo_suspend(struct device *dev)
 	chip->dsp_code = NULL;
 	free_irq(chip->irq, chip);
 	chip->irq = -1;
+	chip->card->sync_irq = -1;
 	return 0;
 }
 
@@ -2204,6 +2206,7 @@ static int snd_echo_resume(struct device *dev)
 		return -EBUSY;
 	}
 	chip->irq = pci->irq;
+	chip->card->sync_irq = chip->irq;
 	dev_dbg(dev, "resume irq=%d\n", chip->irq);
 
 #ifdef ECHOCARD_HAS_MIDI