drm/vc4: Fix -ERESTARTSYS error return from BO waits.

This caused the wait ioctls to claim that waiting had completed when
we actually got interrupted by a signal before it was done.  Fixes
broken rendering throttling that produced serious lag in X window
dragging.

Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
index 3bf679d..15619db 100644
--- a/drivers/gpu/drm/vc4/vc4_gem.c
+++ b/drivers/gpu/drm/vc4/vc4_gem.c
@@ -340,12 +340,10 @@
 	finish_wait(&vc4->job_wait_queue, &wait);
 	trace_vc4_wait_for_seqno_end(dev, seqno);
 
-	if (ret && ret != -ERESTARTSYS) {
+	if (ret && ret != -ERESTARTSYS)
 		DRM_ERROR("timeout waiting for render thread idle\n");
-		return ret;
-	}
 
-	return 0;
+	return ret;
 }
 
 static void