[media] sh_vou: Use video_drvdata()

Replace video_devdata() followed by video_get_drvdata() calls with
video_drvdata().

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>