drm/bridge: add warning for bridges using neither devm_drm_bridge_alloc() nor drm_bridge_add()

The correct sequence for bridge initialization is:

1. devm_drm_bridge_alloc()
2. drm_bridge_add()
3. drm_bridge_attach()

For bridges missing either 1 or 2 there are warnings in place already,
presenting an explanatory error message.

Bridges missing both 1 and 2 would still face a poorly understandable
message, as reported in a recent regression report [0]:

WARNING: [...] at [...]/lib/refcount.c:25 drm_bridge_attach+0x2c/0x1dc
...
Call trace:
...
drm_bridge_attach
...

Add a new warning to ensure an understandable message is logged in such
cases. Use the same message and warning message already in place in
drm_bridge_add().

[0] https://lore.kernel.org/all/hlf4wdopapxnh4rekl5s3kvoi6egaga3lrjfbx6r223ar3txri@3ik53xw5idyh/

Reviewed-by: Maxime Ripard <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Luca Ceresoli <[e-mail]>

drivers/gpu/drm/drm_bridge.c

···
 	if (!encoder || !bridge)
 		return -EINVAL;
 
+	if (!bridge->container)
+		DRM_WARN("DRM bridge corrupted or not allocated by devm_drm_bridge_alloc()\n");
+
 	if (list_empty(&bridge->list))
 		DRM_WARN("Missing drm_bridge_add() before attach\n");