MDEV-33549: Incorrect handling of UPDATE in PS mode in case a table's colum declared as NOT NULL

Follow-up to fix comiler warings caused by present of
the clause override in declaration of the method Item_param::cleanup

sql/item.h

@@ -4000,7 +4000,7 @@ class Item_param :public Item_basic_value,
   Item_param(THD *thd, const LEX_CSTRING *name_arg,
              uint pos_in_query_arg, uint len_in_query_arg);
 
-  void cleanup() override
+  void cleanup()
   {
     m_default_field= NULL;
     Item::cleanup();