greybus: audio: acquire wakelock during active playback

This change was missed while merging original patch
commit-id: 53c765c33f4a69c31027ec012e717d303bd4feca
Thus submitting it again.
Signed-off-by: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/audio_codec.c

@@ -410,6 +410,7 @@ static void gbcodec_shutdown(struct snd_pcm_substream *substream,
 	if (list_empty(&codec->module_list)) {
 		dev_err(codec->dev, "No codec module available\n");
 		mutex_unlock(&codec->lock);
+		pm_relax(dai->dev);
 		return;
 	}