Fix warnings that cause main to fail CI.

Author: manon-traverse

lib/API/DX/Device.cpp

@@ -2373,7 +2373,7 @@ class DXDevice : public offloadtest::Device {
         for (const ResourceSet &RS : R.second) {
           if (RS.Readback == nullptr)
             continue;
-          DXBuffer &ReadbackDX = llvm::cast<DXBuffer>(*RS.Readback);
+          const DXBuffer &ReadbackDX = llvm::cast<DXBuffer>(*RS.Readback);
           addReadbackBeginBarrier(IS, RS.Buffer);
           const CD3DX12_TEXTURE_COPY_LOCATION DstLoc(ReadbackDX.Buffer.Get(),
                                                      Footprint);
@@ -2386,7 +2386,7 @@ class DXDevice : public offloadtest::Device {
       for (const ResourceSet &RS : R.second) {
         if (RS.Readback == nullptr)
           continue;
-        DXBuffer &ReadbackDX = llvm::cast<DXBuffer>(*RS.Readback);
+        const DXBuffer &ReadbackDX = llvm::cast<DXBuffer>(*RS.Readback);
         addReadbackBeginBarrier(IS, RS.Buffer);
         IS.CB->CmdList->CopyResource(ReadbackDX.Buffer.Get(), RS.Buffer.Get());
         addReadbackEndBarrier(IS, RS.Buffer);