net: dsa: mv88e6xxx: Fix ATU age timer for MV88E6390

The MV88E6390 family uses a different ATU age timer coefficient.
Fix the info structures.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>