BTS_Tests: fix log line (AGCH->PCH)

The testcase TC_pcu_data_req_imm_ass_pch uses the PCH to transmit the
IMMEDIATE ASSIGNMENT message but the log line mentions the AGCH.

Related: OS#5927
Change-Id: I7cb8d91f2c3f92009d33134167eab856ee02fdab
diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index c5cc9c7..1ab0f8a 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -5859,7 +5859,7 @@
 		}
 	[] L1CTL.receive { repeat; }
 	[] T.timeout {
-		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail, "Timeout waiting for PCU-originated AGCH block on Um");
+		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail, "Timeout waiting for PCU-originated PCH block on Um");
 		}
 	}
 }