Input: xpad - don't use literal blocks inside footnotes

Unfortunately, Sphinx (or LaTeX) can't handle literal blocks inside
footnotes. So, just use normal text for the two literal code-blocks that
documents the output of /sys/kernel/debug/usb/devices for xpad devices.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>