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/reference_type_propagation.cc b/compiler/optimizing/reference_type_propagation.cc
index 3dfd728..965d5ee 100644
--- a/compiler/optimizing/reference_type_propagation.cc
+++ b/compiler/optimizing/reference_type_propagation.cc
@@ -816,10 +816,10 @@
 void ReferenceTypePropagation::UpdatePhi(HPhi* instr) {
   DCHECK(instr->IsLive());
 
-  auto&& inputs = instr->GetInputs();
+  HInputsRef inputs = instr->GetInputs();
   size_t first_input_index_not_null = 0;
   while (first_input_index_not_null < inputs.size() &&
-      inputs[first_input_index_not_null]->IsNullConstant()) {
+         inputs[first_input_index_not_null]->IsNullConstant()) {
     first_input_index_not_null++;
   }
   if (first_input_index_not_null == inputs.size()) {