ASoC: dapm: Check for NULL widget in dapm_update_dai_unlocked

DAIs linked to the dummy will not have an associated playback/capture
widget, so we need to skip the update in that case.

Fixes: 078a85f2 ("ASoC: dapm: Only power up active channels from a DAI")
Reported-by: NKrzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: NCharles Keepax <ckeepax@opensource.cirrus.com>
Tested-by: NSylwester Nawrocki <s.nawrocki@samsung.com>
Tested-by: NKrzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

sound/soc/soc-dapm.c

@@ -2580,6 +2580,9 @@ static int dapm_update_dai_unlocked(struct snd_pcm_substream *substream,
 	else
 		w = dai->capture_widget;
 
+	if (!w)
+		return 0;
+
 	dev_dbg(dai->dev, "Update DAI routes for %s %s\n", dai->name,
 		dir == SNDRV_PCM_STREAM_PLAYBACK ? "playback" : "capture");