[AMDGPU][SIInsertWaitCnts] Remove redundant TII/TRI/MRI arguments (NFC) (#161357)
WaitCntBrackets already has a pointer to its SIInsertWaitCnt instance.
With a small change, it can directly access TII/TRI/MRI that way.
This simplifies a lot of call sites which make the code easier to
follow.