net: dsa: mv88e6xxx: mv88e6161 uses mv88e6320 stats snapshot

The mv88e6161 was using the wrong method to perform statistics
snapshot.

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>