CVE-2025-39868 erofs: fix runtime warning on truncate_folio_batch_exceptionals()

In the Linux kernel, the following vulnerability has been resolved: erofs: fix runtime warning on truncatefoliobatchexceptionals Commit 0e2f80afcfa6"fs/dax: ensure all pages are idle prior to filesystem unmount" introduced the WARNONONCE to capture whether the filesystem has removed all DAX entri...