dm: fix include guard

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>

include/dm/util.h

@@ -5,6 +5,7 @@
  */
 
 #ifndef __DM_UTIL_H
+#define __DM_UTIL_H
 
 void dm_warn(const char *fmt, ...);