ALSA: Fix debugfs_create_dir's error checking method for sound/soc/

debugfs_create_dir() returns NULL if an error occurs, returns -ENODEV
when debugfs is not enabled in the kernel.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/soc/soc-dapm.c

@@ -831,7 +831,7 @@ int snd_soc_dapm_sys_add(struct device *dev)
 		return ret;
 
 	asoc_debugfs = debugfs_create_dir("asoc", NULL);
-	if (!IS_ERR(asoc_debugfs))
+	if (!IS_ERR(asoc_debugfs) && asoc_debugfs)
 		debugfs_create_u32("dapm_pop_time", 0744, asoc_debugfs,
 				   &pop_time);
 	else