MIPS: Loongson1B: Update stmmac_mdio_bus_data

Update stmmac_mdio_bus_data accordingly due to the upstream change.

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Patchwork: http://patchwork.linux-mips.org/patch/4433


Signed-off-by: John Crispin <blogic@openwrt.org>