Inside mdio_register, a read of the PHY's id register is attempted.
If it fails, we print an error message with eqos_err, which uses the
ethernet device's unique name, but at this time there has been none set,
because eth_register was not yet called. Fix this by using the MDIO bus
device instead.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>