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/pretty_printer.h b/compiler/optimizing/pretty_printer.h
index f9bef68..5891350 100644
--- a/compiler/optimizing/pretty_printer.h
+++ b/compiler/optimizing/pretty_printer.h
@@ -39,7 +39,7 @@
   }
 
   void PrintPostInstruction(HInstruction* instruction) {
-    auto&& inputs = instruction->GetInputs();
+    HConstInputsRef inputs = instruction->GetInputs();
     if (!inputs.empty()) {
       PrintString("(");
       bool first = true;