Replace include guards with #pragma once

Change-Id: I16adc78d397e3239440206e8e70ebbd5e0963adb
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/hwmon.hpp b/hwmon.hpp
index f41c53e..c822045 100644
--- a/hwmon.hpp
+++ b/hwmon.hpp
@@ -1,5 +1,4 @@
-#ifndef __HWMON_H
-#define __HWMON_H
+#pragma once
 
 #include <string>
 
@@ -20,6 +19,4 @@
 }
 }
 
-#endif
-
 // vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4