Added missing const modifier
Added missing const modifier

On Windows in method SerialPortInfo::availablePorts() added a const modifier for the handle of device info.

Change-Id: Id3e0c712fdb01abe9477f8cec78406283efc18bd
Reviewed-by: Laszlo Papp <2164cc32668ec579454611fc5261234262c80421@kde.org>
Reviewed-by: Denis Shienkov <1ad2dee90c89b865e4a01188e9919a005e3f77cf@yandex.ru>

kobolabs/qtserialport,kobolabs/qtserialport,RoadWorksSoftware/QtSerialPort-OS2,RoadWorksSoftware/QtSerialPort-OS2