bmc/test: add missing util header

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I384e9d34d65336c9081da88e4378a987b26c8504
diff --git a/bmc/test/firmware_unittest.hpp b/bmc/test/firmware_unittest.hpp
index 445523c..e9db343 100644
--- a/bmc/test/firmware_unittest.hpp
+++ b/bmc/test/firmware_unittest.hpp
@@ -5,6 +5,7 @@
 #include "flags.hpp"
 #include "image_mock.hpp"
 #include "triggerable_mock.hpp"
+#include "util.hpp"
 
 #include <memory>
 #include <string>