[llvm] [AMDGPU][SIInsertWaitcnts][NFC] Clean up loop (PR #179572)

[via llvm-commits]

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@@ -3010,35 +3010,33 @@ bool SIInsertWaitcnts::insertWaitcntInBlock(MachineFunction &MF,
   MachineInstr *OldWaitcntInstr = nullptr;
   AtomicRMWState RMWState = AtomicRMWState::NotInBlock;
 
-  for (MachineBasicBlock::instr_iterator Iter = Block.instr_begin(),
-                                         E = Block.instr_end();
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vporpo wrote:

True, I will revert to the original `E = Block.instr_end()` for this patch and perhaps change it in a separate patch.

https://github.com/llvm/llvm-project/pull/179572