tools/virtio: fix smp_mb on x86

Offset 128 overlaps the last word of the redzone.
Use 132 which is always beyond that.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/virtio/ringtest/main.h

@@ -111,7 +111,7 @@ static inline void busy_wait(void)
 } 
 
 #if defined(__x86_64__) || defined(__i386__)
-#define smp_mb()     asm volatile("lock; addl $0,-128(%%rsp)" ::: "memory", "cc")
+#define smp_mb()     asm volatile("lock; addl $0,-132(%%rsp)" ::: "memory", "cc")
 #else
 /*
  * Not using __ATOMIC_SEQ_CST since gcc docs say they are only synchronized