[Zucchini]: Fix local shadow error.

In trying to port Zucchini to build elsewhere a -Wshadow error occurred
this is a fix for that.

Change-Id: I8534756e8ee675704e7468bf5512b4e45ec599de
Reviewed-on: https://chromium-review.googlesource.com/967110Reviewed-by: Samuel Huang <huangs@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@google.com>
Cr-Commit-Position: refs/heads/master@{#543816}

components/zucchini/zucchini_tools.cc

@@ -56,7 +56,7 @@ status::Code ReadReferences(ConstBufferView image,
     out << std::endl;
 
     if (do_dump) {
-      auto refs = group.GetReader(disasm.get());
+      refs = group.GetReader(disasm.get());
 
       for (auto ref = refs->GetNext(); ref; ref = refs->GetNext()) {
         out << "  " << AsHex<8>(ref->location);