lavapipe: fix wsi acquire fences

Fixes:
dEQP-VK.wsi.xcb.swapchain.acquire.too_many

Cc: "20.3" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7705>
(cherry picked from commit f24645653863564eb059c1200a52b25f659216e5)
2 files changed