Fix warning

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/thread/ThreadLocalNodes.java

@@ -72,12 +72,12 @@ PDict get(VirtualFrame frame, PThreadLocal self,
         }
 
         @TruffleBoundary
-        private PDict getStorage(PThreadLocal self) {
+        private static PDict getStorage(PThreadLocal self) {
             return self.getThreadLocalDict().get();
         }
 
         @TruffleBoundary
-        private void setStorage(PThreadLocal self, PDict storage) {
+        private static void setStorage(PThreadLocal self, PDict storage) {
             self.getThreadLocalDict().set(storage);
         }
     }