The current Linux Driver and u-boot driver are incapable of running in 10BT mode. The code is incorrect.
There will be a BSP release later with both 100BT and 10BT working. However the messages you are seeing are kernel debug messages saying the buffer has overflowed since the m54455 thinks the 10BT packet was supposed to be 100BT. No hardware modifications are necessary.
Today just live with it. The patch is available to fix fec.c but if you don't need it this month just wait.
Cheers