SGSN_Tests: correct verdict failure message in f_detach_mo()

Change-Id: I5c03ef7dd7486025d35d4482a7fe150dd36de907
diff --git a/sgsn/SGSN_Tests.ttcn b/sgsn/SGSN_Tests.ttcn
index d081360..f5fb21b 100644
--- a/sgsn/SGSN_Tests.ttcn
+++ b/sgsn/SGSN_Tests.ttcn
@@ -909,7 +909,7 @@
 		}
 	[power_off] BSSGP[bssgp_index].receive(tr_BD_L3_MT(tr_GMM_DET_ACCEPT_MT)) -> value bd {
 		g_pars.ra := omit;
-		setverdict(fail, "Unexpected ATTACH ACCEPT in no-power-off DETACH");
+		setverdict(fail, "Unexpected DETACH ACCEPT in power-off DETACH");
 		mtc.stop;
 		/* TODO: check if any PDP contexts are deactivated on network side? */
 		}