ucc_geth: Change uec phy id to the same format as gianfar's

The commit b31a1d8b ("gianfar: Convert
gianfar to an of_platform_driver") changes the gianfar's phy id to the
format like "mdio@xxxx:xx", but uec still uses the old format like
"xxxxxxxx:xx".  For the board whose UEC uses gianfar-mdio like
MPC8568MDS, the phy can not be attached because of the incompatible
phy id format. This patch changes uec's phy id to the same format as
gianfar's.

Signed-off-by: Haiying Wang <Haiying.Wang@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>