[media] omap_vout: remove extra include

Remove including plat/dma.h which is not needed.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>