m68knommu: avoid unneccessary use of xchg() in set_mb()

Avoid unneccessary use of xchg() in set_mb().
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-m68knommu/system.h

@@ -104,7 +104,7 @@ asmlinkage void resume(void);
 #define mb()   asm volatile (""   : : :"memory")
 #define rmb()  asm volatile (""   : : :"memory")
 #define wmb()  asm volatile (""   : : :"memory")
-#define set_mb(var, value) do { xchg(&var, value); } while (0)
+#define set_mb(var, value)	({ (var) = (value); wmb(); })
 
 #ifdef CONFIG_SMP
 #define smp_mb()	mb()