5045 use atomic_{inc,dec}_* instead of atomic_add_*

*** 2400,2410 ****
   */
  void
  snf_vmap_desbfree(snf_vmap_desbinfo *snfv)
  {
          ASSERT(snfv->snfv_ref != 0);
!         if (atomic_add_32_nv(&snfv->snfv_ref, -1) == 0) {
                  vpm_unmap_pages(snfv->snfv_vml, S_READ);
                  VN_RELE(snfv->snfv_vp);
                  kmem_free(snfv, sizeof (snf_vmap_desbinfo));
          }
  }
--- 2400,2410 ----
   */
  void
  snf_vmap_desbfree(snf_vmap_desbinfo *snfv)
  {
          ASSERT(snfv->snfv_ref != 0);
!         if (atomic_dec_32_nv(&snfv->snfv_ref) == 0) {
                  vpm_unmap_pages(snfv->snfv_vml, S_READ);
                  VN_RELE(snfv->snfv_vp);
                  kmem_free(snfv, sizeof (snf_vmap_desbinfo));
          }
  }