Fix the serial number display in the terminal example

The display code was left out in commit
959775c41683033adbd99faab7e3d70e0009c143.

Tested using FTDI device on Windows 8 with Qt5 and
then on Windows 7 with Qt4.

Change-Id: I9f665b2826ba03877346b25a569ca89b6a3dc4af
Reviewed-by: Laszlo Papp <lpapp@kde.org>
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>