net: uec_phy: handle 88e1111 rev.B2 erratum 5.6

erratum 5.6 states the autoneg completion bit is functional only if the
autoneg bit is asserted.

This fixes any secondarily-issued networking commands on non-gigabit
links on the mpc8360 mds board.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>