Documentation: update Michael K. Johnson's work

The URL for "Writing Linux Device Drivers" hasn't been available in some
time. Updating the entry to Michael K. Johnson's "Linux Kernel Hackers'
Guide"

Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
1 file changed