NFS: Cleanup unused rpc_clnt variable

The root rpc_clnt is not used here, clean it up.

Fixes: 4dc73c67

 ("NFSv4: keep state manager thread active if swap is enabled")
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>