5042 stop using deprecated atomic functions

*** 1443,1453 ****
           * we set up the initial call to fss_update() here. Use an atomic
           * compare-and-swap since that's easier and faster than a mutex
           * (but check with an ordinary load first since most of the time
           * this will already be done).
           */
!         if (fssexists == 0 && cas32(&fssexists, 0, 1) == 0)
                  (void) timeout(fss_update, NULL, hz);
  
          return (0);
  }
  
--- 1443,1453 ----
           * we set up the initial call to fss_update() here. Use an atomic
           * compare-and-swap since that's easier and faster than a mutex
           * (but check with an ordinary load first since most of the time
           * this will already be done).
           */
!         if (fssexists == 0 && atomic_cas_32(&fssexists, 0, 1) == 0)
                  (void) timeout(fss_update, NULL, hz);
  
          return (0);
  }