drm/mgag200: Remove disable handling from atomic_update

The primary plane has the atomic_disable helper set, so atomic_update
won't be called if the plane gets disabled. Remove the respective branch
from the helper.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230209154107.30680-4-tzimmermann@suse.de

drivers/gpu/drm/mgag200/mgag200_mode.c

@@ -503,9 +503,6 @@ void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
 	struct drm_rect damage;
 	u8 seq1;
 
-	if (!fb)
-		return;
-
 	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
 	drm_atomic_for_each_plane_damage(&iter, &damage) {
 		mgag200_handle_damage(mdev, shadow_plane_state->data, fb, &damage);