mlxsw: spectrum_switchdev: Do not set 'multicast_enabled' twice

The function mlxsw_sp_port_mc_disabled_set() sets
'bridge_device->multicast_enabled' twice. Remove the unnecessary setting.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>