drm/client: Fix: drm_client_new: Don't require DRM to be registered

Commit 894a677f4b3e ("drm/cma-helper: Use the generic fbdev emulation")
broke almost all drivers that use the CMA helper.

The reason is that drm_client_new() requires that the DRM device has
been registered, but the drivers register fbdev before registering DRM.

Remove the requirement that DRM should be registered when creating a
new client.

Fixes: c76f0f7cb546 ("drm: Begin an API for in-kernel clients")
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Icenowy Zheng <icenowy@aosc.io>
Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180711155632.37437-1-noralf@tronnes.org

drivers/gpu/drm/drm_client.c

@@ -78,7 +78,6 @@ EXPORT_SYMBOL(drm_client_close);
 int drm_client_new(struct drm_device *dev, struct drm_client_dev *client,
 		   const char *name, const struct drm_client_funcs *funcs)
 {
-	bool registered;
 	int ret;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET) ||
@@ -97,21 +96,13 @@ int drm_client_new(struct drm_device *dev, struct drm_client_dev *client,
 		goto err_put_module;
 
 	mutex_lock(&dev->clientlist_mutex);
-	registered = dev->registered;
-	if (registered)
-		list_add(&client->list, &dev->clientlist);
+	list_add(&client->list, &dev->clientlist);
 	mutex_unlock(&dev->clientlist_mutex);
-	if (!registered) {
-		ret = -ENODEV;
-		goto err_close;
-	}
 
 	drm_dev_get(dev);
 
 	return 0;
 
-err_close:
-	drm_client_close(client);
 err_put_module:
 	if (funcs)
 		module_put(funcs->owner);