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>

drivers/gpu/drm/vc4/vc4_gem.c

@@ -340,12 +340,10 @@ vc4_wait_for_seqno(struct drm_device *dev, uint64_t seqno, uint64_t timeout_ns,
 	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