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

@@ -365,17 +365,17 @@
  */
 
 static void
 fem_addref(struct fem_list *sp)
 {
-        atomic_add_32(&sp->feml_refc, 1);
+        atomic_inc_32(&sp->feml_refc);
 }
 
 static uint32_t
 fem_delref(struct fem_list *sp)
 {
-        return (atomic_add_32_nv(&sp->feml_refc, -1));
+        return (atomic_dec_32_nv(&sp->feml_refc));
 }
 
 static struct fem_list *
 fem_get(struct fem_head *fp)
 {