[media] V4L: dynamically allocate video_device nodes in subdevices

Currently only very few drivers actually use video_device nodes, embedded
in struct v4l2_subdev. Allocate these nodes dynamically for those drivers
to save memory for the rest.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Tested-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index 257da1a..5dd049a 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -534,13 +534,13 @@
 	void *dev_priv;
 	void *host_priv;
 	/* subdev device node */
-	struct video_device devnode;
+	struct video_device *devnode;
 };
 
 #define media_entity_to_v4l2_subdev(ent) \
 	container_of(ent, struct v4l2_subdev, entity)
 #define vdev_to_v4l2_subdev(vdev) \
-	container_of(vdev, struct v4l2_subdev, devnode)
+	video_get_drvdata(vdev)
 
 /*
  * Used for storing subdev information per file handle