Add reference to bus from binding

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/serial.c b/serial.c
index 87524f6..482cedb 100644
--- a/serial.c
+++ b/serial.c
@@ -138,7 +138,7 @@
 	assert(pkt);
 
 	if (valid)
-		mctp_bus_rx(serial->mctp, serial->bus_id, pkt);
+		mctp_bus_rx(serial->mctp, &serial->binding, pkt);
 
 	mctp_pktbuf_free(pkt);
 	serial->rx_pkt = NULL;
@@ -295,7 +295,7 @@
 {
 	assert(serial->fd >= 0);
 	serial->mctp = mctp;
-	serial->bus_id = mctp_register_bus(mctp, &serial->binding, eid);
+	mctp_register_bus(mctp, &serial->binding, eid);
 }
 
 struct mctp_binding_serial *mctp_serial_init(void)