docs-rst: fix verbatim font size on tables

On Sphinx 1.6, fancy boxes are used for verbatim. The sphinx.sty
sets verbatim font is always \small. That causes a problem
inside tables that use smaller fonts, as it can be too big for
the box.

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