net: dsa: mv88e6xxx: Work around mv886e6161 SERDES missing MII_PHYSID2

We already have a workaround for a couple of switches whose internal
PHYs only have the Marvel OUI, but no model number. We detect such
PHYs and give them the 6390 ID as the model number. However the
mv88e6161 has two SERDES interfaces in the same address range as its
internal PHYs. These suffer from the same problem, the Marvell OUI,
but no model number. As a result, these SERDES interfaces were getting
the same PHY ID as the mv88e6390, even though they are not PHYs, and
the Marvell PHY driver was trying to drive them.

Add a special case to stop this from happen.

Reported-by: Chris Healy <Chris.Healy@zii.aero>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>