ceph: fix dentry leak in ceph_readdir_prepopulate

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/inode.c

@@ -1681,7 +1681,6 @@ retry_lookup:
 			if (IS_ERR(realdn)) {
 				err = PTR_ERR(realdn);
 				d_drop(dn);
-				dn = NULL;
 				goto next_item;
 			}
 			dn = realdn;