fs/xfs: Fix grub_xfs_iterate_dir return value in case of failure

fs/xfs: Fix grub_xfs_iterate_dir return value in case of failure

Commit ef7850c757 introduced multiple boundary checks in grub_xfs_iterate_dir()
but handled the error incorrectly returning error code instead of 0.

Also change the error message so that it doesn't match the message
in grub_xfs_read_inode().

Fixes: ef7850c757 (fs/xfs: Fix issues found while fuzzing the XFS filesystem)
Signed-off-by: Egor Ignatov <egori@altlinux.org>
Gbp-Pq: Topic cve-2025-jan
Gbp-Pq: Name fs-xfs-Fix-grub_xfs_iterate_dir-return-value-in-case-of-f.patch