ALSA: aoa: i2sbus: use DECLARE_COMPLETION_ONSTACK() macro

Follow recommendation in Documentation/scheduler/completion.rst and
use macro to declare local 'struct completion'
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200902212133.30964-10-pierre-louis.bossart@linux.intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/aoa/soundbus/i2sbus/pcm.c

@@ -254,12 +254,11 @@ static void i2sbus_wait_for_stop(struct i2sbus_dev *i2sdev,
 				 struct pcm_info *pi)
 {
 	unsigned long flags;
-	struct completion done;
+	DECLARE_COMPLETION_ONSTACK(done);
 	long timeout;
 
 	spin_lock_irqsave(&i2sdev->low_lock, flags);
 	if (pi->dbdma_ring.stopping) {
-		init_completion(&done);
 		pi->stop_completion = &done;
 		spin_unlock_irqrestore(&i2sdev->low_lock, flags);
 		timeout = wait_for_completion_timeout(&done, HZ);