[media] DocBook: fix incorrect code example

The code said for (i = 0; i > 30; ++i) instead of i < 30.

Fix this and clean it up a bit at the same time.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>