mncc: Do not print the BTS at all as it might not be present

In contrast to the previous believe we may not have a conn here
as we are still paging for the sub. Instead of printing the BTS
print the lac where we think the subscriber is located.
diff --git a/openbsc/src/gsm_04_08.c b/openbsc/src/gsm_04_08.c
index df24d2f..cf72e59 100644
--- a/openbsc/src/gsm_04_08.c
+++ b/openbsc/src/gsm_04_08.c
@@ -3048,13 +3048,12 @@
 				if (transt == trans ||
 				    transt->subscr != subscr)
 					continue;
-				DEBUGP(DCC, "(bts %d trx - ts - ti -- sub %s) "
+				DEBUGP(DCC, "(bts - trx - ts - ti -- sub %s) "
 					"Received '%s' from MNCC with "
 					"unallocated channel, paging already "
-					"started.\n",
-					trans->conn->lchan->ts->trx->bts->nr,
+					"started for lac %d.\n",
 					data->called.number,
-					get_mncc_name(msg_type));
+					get_mncc_name(msg_type), subscr->lac);
 				subscr_put(subscr);
 				trans_free(trans);
 				return 0;