drm/<drivers>: don't set driver->dev_priv_size to 0

Especially not on modesetting drivers - this is used to size
the driver private structure for legacy drm buffers.

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/ast/ast_drv.c

@@ -198,7 +198,6 @@ static const struct file_operations ast_fops = {
 
 static struct drm_driver driver = {
 	.driver_features = DRIVER_MODESET | DRIVER_GEM,
-	.dev_priv_size = 0,
 
 	.load = ast_driver_load,
 	.unload = ast_driver_unload,