net/sched: Refactor qdisc_graft() for ingress and clsact Qdiscs

Grafting ingress and clsact Qdiscs does not need a for-loop in
qdisc_graft().  Refactor it.  No functional changes intended.

Tested-by: Pedro Tammela <pctammela@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>