Mauro Carvalho Chehab <mchehab+samsung@kernel.org> found a reference
error in Chinese howto.rst. and further more there more infos of
latexdocs/epubdocs format doc making in English howto.rst.

So I update this part according to latest howto.rst and settled
the correct reference.
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>