5047 don't use atomic_*_nv if you discard the return value

@@ -282,11 +282,11 @@
         db = dn->dn_bonus;
 
         /* as long as the bonus buf is held, the dnode will be held */
         if (refcount_add(&db->db_holds, tag) == 1) {
                 VERIFY(dnode_add_ref(dn, db));
-                (void) atomic_inc_32_nv(&dn->dn_dbufs_count);
+                atomic_inc_32(&dn->dn_dbufs_count);
         }
 
         /*
          * Wait to drop dn_struct_rwlock until after adding the bonus dbuf's
          * hold and incrementing the dbuf count to ensure that dnode_move() sees