8254780: EnterInterpOnlyModeClosure::completed() always returns true

Reviewed-by: sspitsyn, rehn

Author: shipilev

src/hotspot/share/prims/jvmtiEventController.cpp

@@ -224,7 +224,7 @@ class EnterInterpOnlyModeClosure : public HandshakeClosure {
     _completed = true;
   }
   bool completed() {
-    return _completed = true;
+    return _completed;
   }
 };