docs: Instruct LaTeX to cope with deeper nesting

The addition of the XFS online fsck documentation starting with
commit a8f6c2e5

 ("xfs: document the motivation for online fsck design")
added a deeper level of nesting than LaTeX is prepared to deal with.  That
caused a pdfdocs build failure with the helpful "Too deeply nested" error
message buried deeply in Documentation/output/filesystems.log.

Increase the "maxlistdepth" parameter to instruct LaTeX that it needs to
deal with the deeper nesting whether it wants to or not.

Suggested-by: Akira Yokosawa <akiyks@gmail.com>
Tested-by: Akira Yokosawa <akiyks@gmail.com>
Cc: stable@vger.kernel.org # v6.4+
Link: https://lore.kernel.org/linux-doc/67f6ac60-7957-4b92-9d72-a08fbad0e028@gmail.com/
Signed-off-by: Jonathan Corbet <corbet@lwn.net>