NFS: Add memory barriers to the nfs_client->cl_cons_state initialisation

Ensure that a process that uses the nfs_client->cl_cons_state test
for whether the initialisation process is finished does not read
stale data.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index c856298..8f39bb3 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5621,6 +5621,7 @@
 	}
 	if (clp->cl_cons_state < NFS_CS_READY)
 		return -EPROTONOSUPPORT;
+	smp_rmb();
 	return 0;
 }