Documentation/kernel-docs.txt: Improve layouting of book list

The dots at the ends of the list elements introduced
unnecesarry newlines in the "compiled" document.

While this was not "mission critical" it's not nice to look at
either.

[mchehab@s-opensource.com: rebased to apply before rename]

Signed-off-by: Richard Sailer <richard@weltraumpflege.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>