cgroup: call fin_cgroup() on error paths

fini_cgroup umounts a cgyard directory, which is mounted
in prepare_cgroup().

Reported-by: Mr Jenkins
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -1822,8 +1822,8 @@ int cr_restore_tasks(void)
 	if (prepare_cgroup_properties() < 0)
 		goto err;
 
-	fini_cgroup();
 err:
+	fini_cgroup();
 	cr_plugin_fini();
 	return ret;
 }