latest qt4-dev will not build

Change-Id: I723253fb153a1144009579141fa0ce1aca93b648 appears to incorrectly implement changes from change-id 23c89518d1404a4db570fe41f3cc04451703e16f. This results in the following compiler error "qtserialport/src/serialport/qserialport_unix.cpp:402:9: error: 'd' was not declared in this scope
if (d->readBufferMaxSize && result > 0 && !d->isReadNotificationEnabled())" when trying to build from source.

It appears this logic should be implemented in qint64 QSerialPort::readData(char *data, qint64 maxSize) within qserialport.cpp rather than qint64 QSerialPortPrivate::readData(char *data, qint64 maxSize) within qserialport_unix.cpp