qeglfskmsegldevicescreen.cpp: add errno.h include

Compilation failed with clang 3.9.1:
qeglfskmsegldevicescreen.cpp:104:27: error: use of undeclared identifier 'errno'
            qErrnoWarning(errno, "drmModeSetCrtc failed");

Change-Id: I7cf08494359092b9cdac10bb013ac56c3ddf5597
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldevicescreen.cpp

@@ -41,6 +41,7 @@
 #include "qeglfskmsegldevice.h"
 #include <QGuiApplication>
 #include <QLoggingCategory>
+#include <errno.h>
 
 QT_BEGIN_NAMESPACE