ceph: fix dentry leak in ceph_readdir_prepopulate

BugLink: https://bugs.launchpad.net/bugs/1854855

[ Upstream commit c58f450b ]
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/ceph/inode.c

@@ -1515,7 +1515,6 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 			if (IS_ERR(realdn)) {
 				err = PTR_ERR(realdn);
 				d_drop(dn);
-				dn = NULL;
 				goto next_item;
 			}
 			dn = realdn;