xf86drmMode.h: Add header protection

xf86drmMode.h is missing a header protection. xf86drm.h has one so just
copy it and adjust the name.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
diff --git a/xf86drmMode.h b/xf86drmMode.h
index 34f5fb1..991e3f9 100644
--- a/xf86drmMode.h
+++ b/xf86drmMode.h
@@ -33,6 +33,9 @@
  *
  */
 
+#ifndef _XF86DRMMODE_H_
+#define _XF86DRMMODE_H_
+
 #if defined(__cplusplus) || defined(c_plusplus)
 extern "C" {
 #endif
@@ -428,3 +431,5 @@
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
+
+#endif