Rename ObjPtr::Decode to ObjPtr::Ptr

Done to prevent ambiguity with ScopedObjectAccess::Decode.

Bug: 31113334

Test: test-art-host
Change-Id: I07a2497cc9cf66386311798933547471987fc316
diff --git a/runtime/scoped_thread_state_change-inl.h b/runtime/scoped_thread_state_change-inl.h
index cf020d0..1d9f132 100644
--- a/runtime/scoped_thread_state_change-inl.h
+++ b/runtime/scoped_thread_state_change-inl.h
@@ -82,7 +82,7 @@
 template<typename T, typename MirrorType, bool kPoison>
 inline T ScopedObjectAccessAlreadyRunnable::AddLocalReference(
     ObjPtr<MirrorType, kPoison> obj) const {
-  return AddLocalReference<T>(obj.Decode());
+  return AddLocalReference<T>(obj.Ptr());
 }
 
 template<typename T, bool kPoison>