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/register_allocator.cc b/compiler/optimizing/register_allocator.cc
index 4a6b835..9d99668 100644
--- a/compiler/optimizing/register_allocator.cc
+++ b/compiler/optimizing/register_allocator.cc
@@ -753,7 +753,7 @@
   if (defined_by != nullptr && !current->IsSplit()) {
     LocationSummary* locations = defined_by->GetLocations();
     if (!locations->OutputCanOverlapWithInputs() && locations->Out().IsUnallocated()) {
-      auto&& inputs = defined_by->GetInputs();
+      HInputsRef inputs = defined_by->GetInputs();
       for (size_t i = 0; i < inputs.size(); ++i) {
         // Take the last interval of the input. It is the location of that interval
         // that will be used at `defined_by`.