drm/sched: Avoid infinite waits in the drm_sched_entity_destroy() path

If we don't initialize the entity to idle and the entity is never
scheduled before being destroyed we end up with an infinite wait in the
destroy path.

v2:
- Add Steven's R-b
Signed-off-by: NBoris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: NSteven Price <steven.price@arm.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NChristian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/393486/

drivers/gpu/drm/scheduler/sched_entity.c

@@ -73,6 +73,9 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
 
 	init_completion(&entity->entity_idle);
 
+	/* We start in an idle state. */
+	complete(&entity->entity_idle);
+
 	spin_lock_init(&entity->rq_lock);
 	spsc_queue_init(&entity->job_queue);