media: dt-bindings: media: rcar_vin: Use status "okay"

According to the Devicetree Specification, "ok" is not a valid status.

Fixes: 47c71bd6 ("[media] rcar_vin: add devicetree support")

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>