mlxsw: spectrum_flow: Drop an unused field

The field "dev" in struct mlxsw_sp_flow_block_binding is not used. Drop it.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>