mlxsw: spectrum_router: Drop mlxsw_sp arg from counter alloc/free functions

The mlxsw_sp reference is carried by the mlxsw_sp_rif object that is passed
to these functions as well. Just deduce the former from the latter,
and drop the explicit mlxsw_sp parameter. Adapt callers.

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