Style cleanup for ObjPtr<>-ify changes.

Replace "ObjPtr<.> const" with "const ObjPtr<.>".

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 31113334
Change-Id: I5a1c080bc88b091e15ee9eb0bb1ef6f6f290701c
diff --git a/runtime/native/java_lang_ref_Reference.cc b/runtime/native/java_lang_ref_Reference.cc
index fc018d1..b241b1d 100644
--- a/runtime/native/java_lang_ref_Reference.cc
+++ b/runtime/native/java_lang_ref_Reference.cc
@@ -30,15 +30,15 @@
 
 static jobject Reference_getReferent(JNIEnv* env, jobject javaThis) {
   ScopedFastNativeObjectAccess soa(env);
-  ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis);
-  ObjPtr<mirror::Object> const referent =
+  const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis);
+  const ObjPtr<mirror::Object> referent =
       Runtime::Current()->GetHeap()->GetReferenceProcessor()->GetReferent(soa.Self(), ref);
   return soa.AddLocalReference<jobject>(referent);
 }
 
 static void Reference_clearReferent(JNIEnv* env, jobject javaThis) {
   ScopedFastNativeObjectAccess soa(env);
-  ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis);
+  const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis);
   Runtime::Current()->GetHeap()->GetReferenceProcessor()->ClearReferent(ref);
 }