Fix error message in qemudLoadDriverConfig()

* src/qemu/qemu_conf.c: change the error message to refer to
  'cgroup_controllers' instead of 'cgroup_device_acl'

src/qemu/qemu_conf.c

@@ -243,7 +243,7 @@ int qemudLoadDriverConfig(struct qemud_driver *driver,
         for (i = 0, pp = p->list; pp; ++i, pp = pp->next) {
             int ctl;
             if (pp->type != VIR_CONF_STRING) {
-                VIR_ERROR("%s", _("cgroup_device_acl must be a list of strings"));
+                VIR_ERROR("%s", _("cgroup_controllers must be a list of strings"));
                 virConfFree(conf);
                 return -1;
             }