mgcp_e1: fix log output

Its not the E1 timeslot that is updated, its the E1 line instead
(which includes the timeslot)

Change-Id: Ic72cf90ebdba1b5e395089417c6df5b962f8ffc8

src/libosmo-mgcp/mgcp_e1.c

@@ -401,7 +401,7 @@ static int e1_init(struct mgcp_trunk *trunk, uint8_t ts_nr)
 	}
 	rc = e1inp_line_update(e1_line);
 	if (rc < 0) {
-		LOGPTRUNK(trunk, DE1, LOGL_ERROR, "failed to update E1 timeslot %u.\n", ts_nr);
+		LOGPTRUNK(trunk, DE1, LOGL_ERROR, "failed to update E1 line %u.\n", ts_nr);
 		return -EINVAL;
 	}