sysfs: make sysfs_put() ignore NULL sd

Make sysfs_put() ignore NULL sd instead of oopsing.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/sysfs.h

@@ -111,7 +111,7 @@ static inline struct sysfs_dirent * sysfs_get(struct sysfs_dirent * sd)
 
 static inline void sysfs_put(struct sysfs_dirent * sd)
 {
-	if (atomic_dec_and_test(&sd->s_count))
+	if (sd && atomic_dec_and_test(&sd->s_count))
 		release_sysfs_dirent(sd);
 }