os: Recompute whether any clients are ready after check_timers()

If a driver calls AttendClient() from within a timer callback we
need to re-compute the local 'are_ready' to prevent the attended
client from waiting until WaitForSomething() times out.

This is a fix similar to commit 9ed5b263.

Signed-off-by: Damien Leone <dleone@nvidia.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
(cherry picked from commit f33cb4264387ed14a586ba080885b4d21e4aa48b)

os/WaitFor.c

@@ -190,10 +190,11 @@ WaitForSomething(Bool are_ready)
         /* deal with any blocked jobs */
         if (workQueue) {
             ProcessWorkQueue();
-            are_ready = clients_are_ready();
         }
 
         timeout = check_timers();
+        are_ready = clients_are_ready();
+
         if (are_ready)
             timeout = 0;