tslib plugin: remove debug print on old tslib versions

This introduces a dependency on ts_get_eventpath(), which is only
available in tslib 1.15 and newer. This raises the required version to
an unneeded level, so just drop the debug message if the API is not
available.

Change-Id: I4a1cd7abec8d139e70555506d9d21edacf0f4d71
Fixes: QTBUG-78867
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Fabian Vogt <fabian@ritter-vogt.de>

src/platformsupport/input/tslib/qtslib.cpp

@@ -68,7 +68,9 @@ QTsLibMouseHandler::QTsLibMouseHandler(const QString &key,
         return;
     }
 
+#ifdef TSLIB_VERSION_EVENTPATH /* also introduced in 1.15 */
     qCDebug(qLcTsLib) << "tslib device is" << ts_get_eventpath(m_dev);
+#endif
     m_notify = new QSocketNotifier(ts_fd(m_dev), QSocketNotifier::Read, this);
     connect(m_notify, &QSocketNotifier::activated, this, &QTsLibMouseHandler::readMouseData);
 }