[media] v4l: vsp1: Protect against race conditions between get and set format

The subdev userspace API isn't serialized in the core, serialize access
to formats and selection rectangles in the driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>