Add SPDX annotation

Related: OS#3515
Change-Id: I3719bd8dc015569ecd81928fc079e27593cdca09
diff --git a/CommonLibs/PRBS.h b/CommonLibs/PRBS.h
index 0b7bbc3..9235327 100644
--- a/CommonLibs/PRBS.h
+++ b/CommonLibs/PRBS.h
@@ -1,6 +1,8 @@
 /*
  * Copyright (C) 2017 Alexander Chemeris <Alexander.Chemeris@fairwaves.co>
  *
+ * SPDX-License-Identifier: LGPL-2.1+
+ *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either