bsc: Make bsc_queue_for_msc work on the osmo_bsc_sccp_con

The gsm_subscriber_connection can die before the SCCP connection
so we should work on the osmo_bsc_sccp_con.
diff --git a/openbsc/src/bsc/osmo_bsc_api.c b/openbsc/src/bsc/osmo_bsc_api.c
index 8ee857d..1964099 100644
--- a/openbsc/src/bsc/osmo_bsc_api.c
+++ b/openbsc/src/bsc/osmo_bsc_api.c
@@ -42,7 +42,7 @@
 		LOGP(DMSC, LOGL_ERROR, "Failed to allocate response.\n"); \
 		return; \
 	} \
-	bsc_queue_for_msc(conn, resp);
+	bsc_queue_for_msc(conn->sccp_con, resp);
 
 static uint16_t get_network_code_for_msc(struct gsm_network *net)
 {
@@ -155,7 +155,7 @@
 		return 0;
 	}
 
-	bsc_queue_for_msc(conn, resp);
+	bsc_queue_for_msc(conn->sccp_con, resp);
 	return 0;
 }