[clang-sycl-linker] Fix a warning

This patch fixes:

  clang/tools/clang-sycl-linker/ClangSYCLLinker.cpp:368:14: error:
  moving a local object in a return statement prevents copy elision
  [-Werror,-Wpessimizing-move]

Author: kazutakahirata

clang/tools/clang-sycl-linker/ClangSYCLLinker.cpp

@@ -365,7 +365,7 @@ Error runSYCLLink(ArrayRef<std::string> Files, const ArgList &Args) {
     SPVFile.append("_" + utostr(I) + ".spv");
     auto Err = runSPIRVCodeGen(SplitModules[I], Args, SPVFile, C);
     if (Err)
-      return std::move(Err);
+      return Err;
     SplitModules[I] = SPVFile;
   }