pcu: Assign TLLI_UNUSED instead of string literal

Change-Id: I7a505527458ed716b7b0912e88c6fcf58e0ff044
diff --git a/pcu/PCU_Tests.ttcn b/pcu/PCU_Tests.ttcn
index 8294f2a..528ee25 100644
--- a/pcu/PCU_Tests.ttcn
+++ b/pcu/PCU_Tests.ttcn
@@ -311,7 +311,7 @@
 
 testcase TC_pcuif_suspend() runs on RAW_PCU_Test_CT {
 	var octetstring ra_id := enc_RoutingAreaIdentification(mp_gb_cfg.bvc[0].cell_id.ra_id);
-	var GprsTlli tlli := 'FFFFFFFF'O;
+	var GprsTlli tlli := TLLI_UNUSED;
 	timer T;
 
 	/* Initialize NS/BSSGP side */