docs/zh_CN: fix a wrong format

Add a missing markup for the code snippet at the end of lru_sort.rst

Signed-off-by: Zang Leigang <zangleigang@hisilicon.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/20230316024519.27992-1-zangleigang@hisilicon.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>