drm/atomic-helper: WARN if fake_commit->hw_done is not completed as expected

For real commits we WARN if ->hw_done hasn't been completed by the time
drm_atomic_helper_commit_cleanup_done() is called. Let's do the same for
the fake commit.

Signed-off-by: Ville Syrjälä <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Reviewed-by: Maarten Lankhorst <[e-mail]>

drivers/gpu/drm/drm_atomic_helper.c

···
 		spin_unlock(&crtc->commit_lock);
 	}
 
-	if (old_state->fake_commit)
+	if (old_state->fake_commit) {
 		complete_all(&old_state->fake_commit->cleanup_done);
+		WARN_ON(!try_wait_for_completion(&old_state->fake_commit->hw_done));
+	}
 }
 EXPORT_SYMBOL(drm_atomic_helper_commit_cleanup_done);