anv/wsi: signal the semaphore in the acquireNextImage

We seem to have forgotten about the semaphore in the
acquireNextImageInfo.

v2: Signal semaphore/fence regardless of presentation status (Jason)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit edc6606d)