drm: remove redundant minor->device field

Whenever we access minor->device, we are in a minor->kdev->...->fops
callback so the minor->kdev pointer *must* be valid. Thus, simply use
minor->kdev->devt instead of minor->device and remove the redundant field.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_stub.c

@@ -318,7 +318,6 @@ static int drm_minor_register(struct drm_device *dev, unsigned int type)
 	if (minor_id < 0)
 		return minor_id;
 
-	new_minor->device = MKDEV(DRM_MAJOR, minor_id);
 	new_minor->index = minor_id;
 
 	idr_replace(&drm_minors_idr, new_minor, minor_id);