bsc_api.c: fix log string format

Fix string format error introduced by recent commit:

"bsc_api: drop unknown RR messages."
I0a4d311f6939a4fcee59129daa18da4a2ab510ae
e4b0ebb25b

Change-Id: Iab11ec6c44eb235d327b3776d5f1d82267ddadaa

src/libbsc/bsc_api.c

@@ -775,7 +775,7 @@ static void dispatch_dtap(struct gsm_subscriber_connection *conn,
 		default:
 			/* Drop unknown RR message */
 			LOGP(DRR, LOGL_NOTICE,
-			     "%s Dropping %s 04.08 RR message from %s\n",
+			     "%s Dropping %s 04.08 RR message\n",
 			     gsm_lchan_name(conn->lchan), gsm48_rr_msg_name(msg_type));
 		}
 		break;