ARM: sunxi: Mask off phy probe for address 0x0

The RTL8211E phy used on the CubieTruck with GMAC in RGMII mode
responds to commands for phy address 0x0 regardless of it's own
address. According to RTL8211E datasheet, phy address 0x0 is
considered the broadcast address.

Mask phy address 0x0 from mdio bus probe.