Xext: dpms: need to include geext.h

It's calling GERegisterExtension(), which is defined in geext.h

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <xorg/xserver!1810>

Xext/dpms.c

@@ -32,6 +32,7 @@ Equipment Corporation.
 #include <X11/Xproto.h>
 
 #include "os/screensaver.h"
+#include "Xext/geext.h"
 
 #include "misc.h"
 #include "os.h"