Address missing variable definition to fix the build.

It was removed by another CL merged just before the
offending CL.

Test: m build-art-host
Bug: 29516974
Bug: 29506760
Bug: 12687968
Change-Id: I4457b6dafd48731eef5c8cc370d9107764d6f55c
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index d50b786..17fc13c 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -2171,7 +2171,7 @@
   } else {
     locations->SetInAt(2, Location::RequiresRegister());
   }
-  if (object_array_set_with_read_barrier && kUseBakerReadBarrier) {
+  if (kEmitCompilerReadBarrier && kUseBakerReadBarrier && (value_type == Primitive::kPrimNot)) {
     // Additional temporary registers for a Baker read barrier.
     locations->AddTemp(Location::RequiresRegister());
     locations->AddTemp(Location::RequiresRegister());