[AMDGPU] Drop const for value that is copied (NFC).

This fixes

    warning: loop variable 'Def' of type 'const llvm::Register' creates a copy from type 'const llvm::Register' [-Wrange-loop-analysis]

llvm::Register just contains a single unsigned and should be copied.

Reviewers: rampitec

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D77011

llvm/lib/Target/AMDGPU/SIPostRABundler.cpp

@@ -76,7 +76,7 @@ bool SIPostRABundler::isDependentLoad(const MachineInstr &MI) const {
     if (!Op.isReg())
       continue;
     Register Reg = Op.getReg();
-    for (const Register Def : Defs)
+    for (Register Def : Defs)
       if (TRI->regsOverlap(Reg, Def))
         return true;
   }