Fix compilation with clang, missing errno.h

Similar to cfe1a295fc which was in a different file.

Change-Id: I40e204f8603a2d4c10a6c737192957653f537d1a
Reviewed-by: Jake Petroules <jake.petroules@qt.io>

src/platformsupport/kmsconvenience/qkmsdevice.cpp

@@ -47,6 +47,8 @@
 #include <QtCore/QFile>
 #include <QtCore/QLoggingCategory>
 
+#include <errno.h>
+
 #define ARRAY_LENGTH(a) (sizeof (a) / sizeof (a)[0])
 
 QT_BEGIN_NAMESPACE