sh_eth: Register MDIO bus before registering the network device

Network API functions that rely on the MDIO bus can be called as soon as
the driver calls register_netdev(). Register the MDIO bus before the
network device to avoid race conditions.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: David S. Miller <davem@davemloft.net>