The old link to source code cross reference does not work now. Though
the link has updated by commit 1d12554f
("Documentation: HOWTO: update code cross reference link"), there are
few obsolete links yet. This commit update them.
Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>