radv: Fix timeline semaphore refcounting.

Was totally broken ...

Removed two if(point) {} because point is always non-NULL and we
were counting on that already for counting, since we NULL our
references to semaphores without active point earlier.

Fixes: 4aa75bb3 "radv: Add wait-before-submit support for timelines."
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2137


Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
(cherry picked from commit 48fc6541)