Same problem as in stdu, same fix.

Fixes: 51f644b4 ("drm/atomic-helper: reset vblank on crtc reset")
Acked-by: NCharmaine Lee <charmainel@vmware.com>
Reviewed-by: NZack Rusin <zackr@vmware.com>
Signed-off-by: NRoland Scheidegger <sroland@vmware.com>