bsc: release dchan in TC_cbsp_emerg_write_bts_cgi_dchan

A follow-up patch is adding BSC_Tests.f_shutdown_helper() calls to all
CBSP testcases, what makes TC_cbsp_emerg_write_bts_cgi_dchan fail due
to talloc count mismatch.  All dchans need to be released to avoid this.

Change-Id: I8b707c821693f930ab10bd8feea08ba5007da967
diff --git a/bsc/BSC_Tests_CBSP.ttcn b/bsc/BSC_Tests_CBSP.ttcn
index e38b8a6..61b2efd 100644
--- a/bsc/BSC_Tests_CBSP.ttcn
+++ b/bsc/BSC_Tests_CBSP.ttcn
@@ -971,6 +971,8 @@
 		setverdict(fail, "Waiting for APP INFO");
 		}
 	}
+
+	f_perform_clear_test_ct(dt);
 }
 
 private function f_exp_rsl_etws(integer rsl_idx := 0, boolean enabled) runs on cbsp_test_CT {