media: rcar-vin: Rename wrongly named rectangle

After recent refactoring the rectangle named crop no longer reflects it
usage, to contain the source rectangle. Fix this by renaming it. There
is no functional change.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>