loop: Properly clear sysfs in autoclear mode

In autoclear mode bdev is NULL but the sysfs
entry should be destroyed otherwise this warning appears:

WARNING: at fs/sysfs/dir.c:451 sysfs_add_one+0x82/0x95()
sysfs: cannot create duplicate filename '/devices/virtual/block/loop0/loop'

Fixes commit ee862730Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

drivers/block/loop.c

@@ -1049,9 +1049,9 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
 	if (bdev)
 		invalidate_bdev(bdev);
 	set_capacity(lo->lo_disk, 0);
+	loop_sysfs_exit(lo);
 	if (bdev) {
 		bd_set_size(bdev, 0);
-		loop_sysfs_exit(lo);
 		/* let user-space know about this change */
 		kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
 	}