multistreamserver: fix compilation

Instead of including <QIODevice>, use the correct 'nested name
specifier', QIODeviceBase.

Amends 8bd0a09475935cf33f6b7f63a898d4d2e6d43b17.

Pick-to: 6.2
Change-Id: I077948b33f985cd4a2e3a9e591645cf20d7af91c
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

examples/network/multistreamserver/timeprovider.cpp

@@ -71,7 +71,7 @@ void TimeProvider::readDatagram(QSctpSocket &from, const QByteArray &ba)
         || curTime.minute() != clientTime.minute()
         || curTime.hour() != clientTime.hour()) {
         QByteArray buf;
-        QDataStream out_ds(&buf, QIODevice::WriteOnly);
+        QDataStream out_ds(&buf, QIODeviceBase::WriteOnly);
 
         out_ds << curTime;
         emit writeDatagram(&from, buf);