nfsd4: Fix forced-expiry locking

This should use the network-namespace-wide client_lock, not the
per-client cl_lock.

You shouldn't see any bugs unless you're actually using the
forced-expiry interface introduced by 89c905be.

Fixes: 89c905be "nfsd: allow forced expiration of NFSv4 clients"
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -2687,9 +2687,9 @@ static void force_expire_client(struct nfs4_client *clp)
 
 	trace_nfsd_clid_admin_expired(&clp->cl_clientid);
 
-	spin_lock(&clp->cl_lock);
+	spin_lock(&nn->client_lock);
 	clp->cl_time = 0;
-	spin_unlock(&clp->cl_lock);
+	spin_unlock(&nn->client_lock);
 
 	wait_event(expiry_wq, atomic_read(&clp->cl_rpc_users) == 0);
 	spin_lock(&nn->client_lock);