ASoC: Check return value of struct_strtoul() in pmdown_time_set()

strict_strtoul() has just been made must check so do so.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index 70d9a73..805343f 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -165,8 +165,11 @@
 {
 	struct snd_soc_pcm_runtime *rtd =
 			container_of(dev, struct snd_soc_pcm_runtime, dev);
+	int ret;
 
-	strict_strtol(buf, 10, &rtd->pmdown_time);
+	ret = strict_strtol(buf, 10, &rtd->pmdown_time);
+	if (ret)
+		return ret;
 
 	return count;
 }