[media] vivid: Local optimization

Avoid duplicated clamps when possible.

Suggested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>