mlxsw: spectrum_switchdev: Remove redundant check

Since commit 97c24290 ("switchdev: Execute bridge ndos only for
bridge ports") switchdev code checks that port is bridged, so no need to
perform the same check in the driver.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>