Fix some typos in Documentation/memory-barriers.txt
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>