serial: Add mctp_serial_destroy()

Provide an abstraction to clean up memory to avoid false-positives from
leak sanitizers.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I3b8b044c81cb5ba99fb91261d5bf952993497dd7
diff --git a/serial.c b/serial.c
index c90de54..f24148a 100644
--- a/serial.c
+++ b/serial.c
@@ -356,3 +356,7 @@
 	return serial;
 }
 
+void mctp_serial_destroy(struct mctp_binding_serial *serial)
+{
+	__mctp_free(serial);
+}