tools/memory-model: Fix typo in klitmus7 compatibility table

klitmus7 of herdtools7 7.48 or earlier depends on ACCESS_ONCE(),
which was removed in Linux v4.15.
Fix the obvious typo in the table.

Fixes: d075a78a ("tools/memory-model/README: Expand dependency of klitmus7")
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>