ceph_fill_trace(): don't bother with d_instantiate(dn, NULL)

... and use d_add(dn, NULL) in case we need to hash a negative
unhashed rather than using d_rehash() directly.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/ceph/inode.c

@@ -1236,10 +1236,8 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req,
 				dout("d_delete %p\n", dn);
 				d_delete(dn);
 			} else {
-				dout("d_instantiate %p NULL\n", dn);
-				d_instantiate(dn, NULL);
 				if (have_lease && d_unhashed(dn))
-					d_rehash(dn);
+					d_add(dn, NULL);
 				update_dentry_lease(dn, rinfo->dlease,
 						    session,
 						    req->r_request_started);