net: fs_enet: Fix an error handling path

'of_node_put(fpi->phy_node)' should also be called if we branch to
'out_deregister_fixed_link' error handling path.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>