Revert "drm/bridge: Fix a NULL pointer dereference in drm_atomic_bridge_chain_check()"

This reverts commit b18398c1 ("drm/bridge: Fix a NULL pointer
dereference in drm_atomic_bridge_chain_check()"). Commit 6ed7e962
("drm/bridge: Add a drm_bridge_state object") introduced a circular
dependency between drm.ko and drm_kms_helper.ko which uncovered a
misdesign in how the whole thing was implemented. Let's revert all
patches depending on the bridge_state infrastructure for now.
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200107185807.606999-2-boris.brezillon@collabora.com

drivers/gpu/drm/drm_bridge.c

@@ -938,19 +938,15 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
 				  struct drm_connector_state *conn_state)
 {
 	struct drm_connector *conn = conn_state->connector;
-	struct drm_encoder *encoder;
+	struct drm_encoder *encoder = bridge->encoder;
 	struct drm_bridge *iter;
 	int ret;
 
-	if (!bridge)
-		return 0;
-
 	ret = drm_atomic_bridge_chain_select_bus_fmts(bridge, crtc_state,
 						      conn_state);
 	if (ret)
 		return ret;
 
-	encoder = bridge->encoder;
 	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
 		int ret;