Create a typedef for HInstruction::GetInputs() return type.

And some other cleanup after
    https://android-review.googlesource.com/230742

Test: No new tests. ART test suite passed (tested on host).
Change-Id: I4743bf17544d0234c6ccb46dd0c1b9aae5c93e17
diff --git a/compiler/optimizing/graph_visualizer.cc b/compiler/optimizing/graph_visualizer.cc
index 4af8d19..9d67373 100644
--- a/compiler/optimizing/graph_visualizer.cc
+++ b/compiler/optimizing/graph_visualizer.cc
@@ -511,7 +511,7 @@
 
   void PrintInstruction(HInstruction* instruction) {
     output_ << instruction->DebugName();
-    auto&& inputs = instruction->GetInputs();
+    HConstInputsRef inputs = instruction->GetInputs();
     if (!inputs.empty()) {
       StringList input_list;
       for (const HInstruction* input : inputs) {