net: dsa: remove trans argument from mdb ops

The DSA switch MDB ops pass the switchdev_trans structure down to the
drivers, but no one is using them and they aren't supposed to anyway.

Remove the trans argument from MDB prepare and add operations.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>