mlxsw: spectrum_qdisc: Drop one argument from check_params callback

The mlxsw_sp_qdisc argument is not used in any of the actual callbacks.
Drop it.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>