bmc_mode: Add #pragma once

This was missed initially

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: I9d7de13bab0e18e1335654f174c5d4564771464f
diff --git a/bmc_mode_enum.hpp b/bmc_mode_enum.hpp
index d264c3a..dbad89b 100644
--- a/bmc_mode_enum.hpp
+++ b/bmc_mode_enum.hpp
@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#pragma once
+
 #include <cstdint>
 
 namespace google