[ALSA] soc - 0.13 ASoC DAPM bug fix for unnamed streams

This patch fixes a bug whereby an unnamed stream would cause a NULL
pointer ref in snd_soc_dapm_stream_event().

Signed-off-by: Seth Forshee <seth.forshee@gmail.com>
Signed-off-by: Liam Girdwood <lg@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/soc/soc-dapm.c

@@ -1239,6 +1239,9 @@ int snd_soc_dapm_stream_event(struct snd_soc_codec *codec,
 {
 	struct snd_soc_dapm_widget *w;
 
+	if (stream == NULL)
+		return 0;
+
 	mutex_lock(&codec->mutex);
 	list_for_each_entry(w, &codec->dapm_widgets, list)
 	{