When au1000_eth probes the MII bus for PHY address, if we do not set
au1000_eth platform data's phy_search_highest_address, the MII probing
logic will exit early and will assume a valid PHY is found at address 0.
For MTX-1, the PHY is at address 31, and without this patch, the link
detection/speed/duplex would not work correctly.

CC: stable@kernel.org
Signed-off-by: NFlorian Fainelli <florian@openwrt.org>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2111/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>