[SCEV] Fix -Wunused-variable in ScalarEvolutionExpander.cpp (NFC)

llvm-project/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp:1077:15: error: unused variable 'Start' [-Werror,-Wunused-variable]
  const SCEV *Start = Normalized->getStart();
              ^
1 error generated.