sh_eth: Use platform device for printing before register_netdev()

The MDIO initialization failure message is printed using the network
device, before it has been registered, leading to:

     (null): failed to initialise MDIO

Use the platform device instead to fix this:

    sh-eth ee700000.ethernet: failed to initialise MDIO

Fixes: daacf03f ("sh_eth: Register MDIO bus before registering the network device")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: David S. Miller <davem@davemloft.net>