mlxsw: spectrum_router: Have mlxsw_sp_nexthop_counter_enable() return int

In order to be able to diagnose failures in counter allocation, have the
function mlxsw_sp_nexthop_counter_enable() return an error code.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/e0bb5c0cc6234ade2ade1e92abac991359c3f446.1709901020.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>