nfsd: return correct lockowner when there is a race on hash insert

alloc_init_lock_stateowner can return an already freed entry if there is
a race to put openowners in the hashtable.

Noticed by inspection after Jeff Layton fixed the same bug for open
owners.  Depending on client behavior, this one may be trickier to
trigger in practice.

Fixes: c58c6610 "nfsd: Protect adding/removing lock owners using client_lock"
Cc: <stable@vger.kernel.org>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Acked-by: NJeff Layton <jeff.layton@primarydata.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -5062,7 +5062,7 @@ alloc_init_lock_stateowner(unsigned int strhashval, struct nfs4_client *clp,
 	} else
 		nfs4_free_lockowner(&lo->lo_owner);
 	spin_unlock(&clp->cl_lock);
-	return lo;
+	return ret;
 }
 
 static void