Fix compilation of apps with QT_DISABLE_DEPRECATED_BEFORE=0x050300

The enum is already marked as deprecated leading to this error:
qserialport.h:267:46: error: no type named 'DataErrorPolicy' in 'QSerialPort'
    void dataErrorPolicyChanged(QSerialPort::DataErrorPolicy policy);
                                ~~~~~~~~~~~~~^

Change-Id: I8d178f0d0921b8f5308183e1f09a4c8388448e26
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>