ASoC: simple-card: fix the DAPM routes map parsing

The simple-card's DAPM route maping is optional.
Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/generic/simple-card.c

@@ -134,10 +134,12 @@ static int asoc_simple_card_parse_of(struct device_node *node,
 		(SND_SOC_DAIFMT_FORMAT_MASK | SND_SOC_DAIFMT_INV_MASK);
 
 	/* DAPM routes */
-	ret = snd_soc_of_parse_audio_routing(&info->snd_card,
+	if (of_property_read_bool(node, "simple-audio-routing")) {
+		ret = snd_soc_of_parse_audio_routing(&info->snd_card,
 					"simple-audio-routing");
-	if (ret)
-		return ret;
+		if (ret)
+			return ret;
+	}
 
 	/* CPU sub-node */
 	ret = -EINVAL;