media: MAINTAINERS: Add co-maintainer for the rkisp1 driver

As I'm actively working on the rkisp1 driver, I would like to volunteer
as a co-maintainer, mostly to make sure I get CC on patches.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>