ice: refactor ice_sched to make functions static

As ice_sched_set_node_bw_lmt_per_tc is not used
outside of ice_sched, it can be made static.

Signed-off-by: Jan Sokolowski <jan.sokolowski@intel.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>