[PATCH] fix typo in memory barrier docs

Fix cut'n'paste typo - &a and &b are used in other examples, in this one
the doc uses &u and &v.
Signed-off-by: NPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Documentation/memory-barriers.txt

@@ -1898,7 +1898,7 @@ queue before processing any further requests:
 	smp_wmb();
 	<A:modify v=2>	<C:busy>
 			<C:queue v=2>
-	p = &b;		q = p;
+	p = &v;		q = p;
 			<D:request p>
 	<B:modify p=&v>	<D:commit p=&v>
 		  	<D:read p>