fdt: Add header guard to fdtdec.h

This makes it easier to include this header from other headers.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/fdtdec.h b/include/fdtdec.h
index a8f783f..d829606 100644
--- a/include/fdtdec.h
+++ b/include/fdtdec.h
@@ -19,6 +19,8 @@
  * MA 02111-1307 USA
  */
 
+#ifndef __fdtdec_h
+#define __fdtdec_h
 
 /*
  * This file contains convenience functions for decoding useful and
@@ -382,3 +384,4 @@
  */
 const u8 *fdtdec_locate_byte_array(const void *blob, int node,
 			     const char *prop_name, int count);
+#endif