powerpc/5200: fix lite5200 ethernet phy address

According to my schematics, on Lite5200 board ethernet phy uses address
0 (all ADDR lines are pulled down). With this change I can talk to
onboard phy (LXT971) and correctly use autonegotiation.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>