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/native/java_lang_VMClassLoader.cc b/runtime/native/java_lang_VMClassLoader.cc
index 0694c4d..73d12f1 100644
--- a/runtime/native/java_lang_VMClassLoader.cc
+++ b/runtime/native/java_lang_VMClassLoader.cc
@@ -40,7 +40,7 @@
   mirror::Class* c = cl->LookupClass(soa.Self(),
                                      descriptor.c_str(),
                                      descriptor_hash,
-                                     loader.Decode());
+                                     loader.Ptr());
   if (c != nullptr && c->IsResolved()) {
     return soa.AddLocalReference<jclass>(c);
   }