net: ethernet: renesas: ravb: fix fixed-link phydev leaks

Make sure to deregister and free any fixed-link PHY registered using
of_phy_register_fixed_link() on initialisation errors and on device
close after having disconnected the PHY.

Fixes: b4bc88a8 ("ravb: Add fixed-link support")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>