add-on fixing: fix some issues

1. 1% kernel build regression. Suggested by Matthew
2. Wrong return value of filemap_map_folio_range()
3. mmap_miss change in filemap_map_folio_range() is overwritten
   by filemap_map_pages(). Ryan pointed out
4. pte_old() vs pte_yong() for prefault folio. Ryan pointed out
   and Matthew suggested the fix
5. typo in folio_add_file_rmap_range()

Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>