Fix comment in sys/sem.h

[Michal Mazurek]

It's _SYS_SEM_H_ not _SEM_H_:

        #ifndef _SYS_SEM_H_
        #define _SYS_SEM_H_

Index: sys/sys/sem.h
===================================================================
RCS file: /cvs/src/sys/sys/sem.h,v
retrieving revision 1.23
diff -u -p -r1.23 sem.h
--- sys/sys/sem.h       23 Nov 2014 04:31:42 -0000      1.23
+++ sys/sys/sem.h       1 Sep 2016 07:22:26 -0000
@@ -195,4 +195,4 @@ int semop(int, struct sembuf *, size_t);
 __END_DECLS
 #endif /* !_KERNEL */
 
-#endif /* !_SEM_H_ */
+#endif /* !_SYS_SEM_H_ */

-- 
Michal Mazurek