Make sure to deregister and free any fixed-link PHY registered using
of_phy_register_fixed_link() on slave-setup errors and on slave destroy.

Fixes: 0d8bcdd3 ("net: dsa: allow for more complex PHY setups")
Signed-off-by: NJohan Hovold <johan@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>