cosmetics: normalize include guards

use the recommended format [1] of:
<PROJECT>_<PATH>_<FILE>_H_

[1] https://google.github.io/styleguide/cppguide.html#The__define_Guard
"All header files should have #define guards to prevent multiple
inclusion. The format of the symbol name should be
<PROJECT>_<PATH>_<FILE>_H_."

Change-Id: I00a0595fc2a5fc736ab6ff3215727d6db05b10e1
diff --git a/tools/obu_parser.h b/tools/obu_parser.h
index 86e7c45..1d7d2d7 100644
--- a/tools/obu_parser.h
+++ b/tools/obu_parser.h
@@ -9,8 +9,8 @@
  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  */
 
-#ifndef TOOLS_OBU_PARSER_H_
-#define TOOLS_OBU_PARSER_H_
+#ifndef AOM_TOOLS_OBU_PARSER_H_
+#define AOM_TOOLS_OBU_PARSER_H_
 
 #include <cstdint>
 
@@ -24,4 +24,4 @@
 
 }  // namespace aom_tools
 
-#endif  // TOOLS_OBU_PARSER_H_
+#endif  // AOM_TOOLS_OBU_PARSER_H_