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/test/454-get-vreg/get_vreg_jni.cc b/test/454-get-vreg/get_vreg_jni.cc
index 9058af4..0360eda 100644
--- a/test/454-get-vreg/get_vreg_jni.cc
+++ b/test/454-get-vreg/get_vreg_jni.cc
@@ -123,7 +123,7 @@
 extern "C" JNIEXPORT jint JNICALL Java_Main_doNativeCall(JNIEnv*, jobject value) {
   ScopedObjectAccess soa(Thread::Current());
   std::unique_ptr<Context> context(Context::Create());
-  TestVisitor visitor(soa.Self(), context.get(), soa.Decode<mirror::Object>(value).Decode());
+  TestVisitor visitor(soa.Self(), context.get(), soa.Decode<mirror::Object>(value).Ptr());
   visitor.WalkStack();
   return visitor.found_method_index_;
 }