net: dsa: mv8e6xxx: fix number of internal PHYs for 88E6x90 family

Ports 9 and 10 don't have internal PHY's but are (dependent on the
version) SERDES/SGMII/XAUI/RXAUI ports.

v2:
- fix it for all 88E6x90 family members

Fixes: bc393155

 ("net: dsa: mv88e6xxx: Add number of internal PHYs")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>