fsl_pq_mdio: Revive UCC MDIO support

commit 1577ecef

 ("netdev: Merge UCC
and gianfar MDIO bus drivers") introduced a regression so that UCC
MDIO buses no longer work.

This is because fsl_pq_mdio driver wrongly masks all non-TBI PHYs
for !fsl,gianfar-mdio buses, while it should do that only for
fsl,gianfar-tbi buses.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>