docs/memory-barriers.txt: Add a missed closing parenthesis

The description of io_stop_wc(), which was added by commit d5624bb2
("asm-generic: introduce io_stop_wc() and add implementation for ARM64"),
has an unclosed parenthesis.  This commit closes it.

Fixes: d5624bb2 ("asm-generic: introduce io_stop_wc() and add implementation for ARM64")
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Documentation/memory-barriers.txt

@@ -1966,7 +1966,7 @@ There are some more advanced barrier functions:
  (*) io_stop_wc();
 
      For memory accesses with write-combining attributes (e.g. those returned
-     by ioremap_wc(), the CPU may wait for prior accesses to be merged with
+     by ioremap_wc()), the CPU may wait for prior accesses to be merged with
      subsequent ones. io_stop_wc() can be used to prevent the merging of
      write-combining memory accesses before this macro with those after it when
      such wait has performance implications.