media: rcar-vin: Do not cache remote rectangle

Prepare for scaling support in the media controller part of the driver
by not caching the remote rectangle. Mimic the omap3isp and look it up
each time it's needed.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>