sh: Warn against direct inclusion of <asm/rwsem.h>.

Signed-off-by: NRobert P. J. Day <rpjday@mindspring.com>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

include/asm-sh/rwsem.h

 /*
- * include/asm-ppc/rwsem.h: R/W semaphores for SH using the stuff
+ * include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
  * in lib/rwsem.c.
  */
 
 #ifndef _ASM_SH_RWSEM_H
 #define _ASM_SH_RWSEM_H
 
+#ifndef _LINUX_RWSEM_H
+#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
+#endif
+
 #ifdef __KERNEL__
 #include <linux/list.h>
 #include <linux/spinlock.h>