NFS: Fix a typo in nfs_rename()

[ Upstream commit d803224c84be067754db7fa58a93f36f61566493 ]

On successful rename, the "old_dentry" is retained and is attached to
the "new_dir", so we need to call nfs_set_verifier() accordingly.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>