media: docs: v4l2-controls: convert code blocks to C

All these code blocks contain C code, enable C formatting for a nicer
reading.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>