6138 don't abuse atomic_cas_*

*** 886,908 ****
  
  /* ARGSUSED */
  uint_t
  get_color_start(struct as *as)
  {
-         uint32_t old, new;
- 
          if (consistent_coloring == 2 || color_start_random) {
                  return ((uint_t)(((gettick()) << (vac_shift - MMU_PAGESHIFT)) &
                      (hw_page_array[0].hp_colors - 1)));
          }
  
!         do {
!                 old = color_start_current;
!                 new = old + (color_start_stride << (vac_shift - MMU_PAGESHIFT));
!         } while (atomic_cas_32(&color_start_current, old, new) != old);
! 
!         return ((uint_t)(new));
  }
  
  /*
   * Called once at startup from kphysm_init() -- before memialloc()
   * is invoked to do the 1st page_free()/page_freelist_add().
--- 886,902 ----
  
  /* ARGSUSED */
  uint_t
  get_color_start(struct as *as)
  {
          if (consistent_coloring == 2 || color_start_random) {
                  return ((uint_t)(((gettick()) << (vac_shift - MMU_PAGESHIFT)) &
                      (hw_page_array[0].hp_colors - 1)));
          }
  
!         return ((uint_t)atomic_add_32_nv(&color_start_current,
!             color_start_stride << (vac_shift - MMU_PAGESHIFT)));
  }
  
  /*
   * Called once at startup from kphysm_init() -- before memialloc()
   * is invoked to do the 1st page_free()/page_freelist_add().