[media] rcar-vin: return correct error from platform_get_irq()

Fix a error from the original driver where the wrong error code is
returned if the driver fails to get a IRQ number from
platform_get_irq().

Signed-off-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>