docs/zh_CN: Fix typo in process/howto.rst

Correct the url of linux-next

Signed-off-by: Zhou Yuheng <woshoxxx@gmail.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Acked-by: Tang Yizhou <tangyizhou@huawei.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>