Through a reply I received from a user here from Stack Overflow in English, this can be found here, I was able to elaborate a function that can perfectly find the coordinates through the address, follows: 
QGeoCoordinate MainWindow::getGeoCoordinates() {
    QEventLoop loop;
    QGeoCoordinate qGeoCoord;
    QStringList qGeoSrvList = QGeoServiceProvider::availableServiceProviders();
    for (QString entry : qGeoSrvList) {
        QGeoServiceProvider qGeoService(entry);
        QGeoCodingManager *pQGeoCoder = qGeoService.geocodingManager();
        if ( ( qGeoService.error() == 0 ) && ( qGeoService.errorString().compare("") == 0 ) ) {
            QLocale qLocaleC(QLocale::C, QLocale::AnyCountry);
            pQGeoCoder->setLocale(qLocaleC);
            QGeoAddress qGeoAddr;
            qGeoAddr.setCountry( "país" );
            qGeoAddr.setPostalCode( "cep" );
            qGeoAddr.setCity( "cidade" );
            qGeoAddr.setStreet( "rua, número" );
            qGeoAddr.setState( "estado" );
            QGeoCodeReply *pQGeoCode = pQGeoCoder->geocode(qGeoAddr);
            connect( pQGeoCode, SIGNAL(finished()), &loop, SLOT(quit()));
            loop.exec();
            if ( pQGeoCode->error() != QGeoCodeReply::NoError ) {
                qDebug() << pQGeoCode->error() << " | " << pQGeoCode->errorString();
                break;
            } else {
                QList<QGeoLocation> qGeoLocs = pQGeoCode->locations();
                for (QGeoLocation &qGeoLoc : qGeoLocs) {
                    qGeoLoc.setAddress(qGeoAddr);
                    qGeoCoord = qGeoLoc.coordinate();
                }
            }
        }
    }
    return qGeoCoord;
}
OBS: Remembering that no . pro should be added QT += Positioning Location