[NFC] Remove dead assignments

[MartinWehking]

Summary

Dest is never used after creating the type making these assignments dead

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

bool AMDGPULegalizerInfo::legalizeSBufferLoad(
   unsigned Size = Ty.getSizeInBits();
   MachineFunction &MF = B.getMF();
 
   Observer.changingInstr(MI);
 
   // Handle needing to s.buffer.load() a p8 value.
   if (hasBufferRsrcWorkaround(Ty)) {
     Ty = castBufferRsrcFromV4I32(MI, B, *B.getMRI(), 0);
-    Dst = MI.getOperand(0).getReg();
     B.setInsertPt(B.getMBB(), MI);
   }
   if (shouldBitcastLoadStoreType(ST, Ty, LLT::scalar(Size))) {
     Ty = getBitcastRegisterType(Ty);
     Helper.bitcastDst(MI, Ty, 0);
-    Dst = MI.getOperand(0).getReg();
     B.setInsertPt(B.getMBB(), MI);
   }
 
   // FIXME: We don't really need this intermediate instruction. The intrinsic
   // should be fixed to have a memory operand. Since it's readnone, we're not
   // allowed to add one.
   MI.setDesc(B.getTII().get(AMDGPU::G_AMDGPU_S_BUFFER_LOAD));
   MI.removeOperand(1); // Remove intrinsic ID