net: ethoc: Fix early error paths

In case any operation fails before we can successfully go the point
where we would register a MDIO bus, we would be going to an error label
which involves unregistering then freeing this yet to be created MDIO
bus. Update all error paths to go to label free which is the only one
valid until either the clock is enabled, or the MDIO bus is allocated
and registered. This fixes kernel oops observed while trying to
dereference the MDIO bus structure which is not yet allocated.

Fixes: a1702857 ("net: Add support for the OpenCores 10/100 Mbps Ethernet MAC.")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>