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/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index 1ddf961..59c4681 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -1566,7 +1566,7 @@
       ScopedObjectAccess soa(self);
       dex_caches_.push_back(soa.AddLocalReference<jobject>(
           class_linker->RegisterDexFile(*dex_file,
-                                        soa.Decode<mirror::ClassLoader>(class_loader_).Decode())));
+                                        soa.Decode<mirror::ClassLoader>(class_loader_).Ptr())));
     }
 
     return true;