Documentation/cgroups/memory.txt: fix typo

It should be memsw.max_usage_in_bytes. This typo has been there for
a really long time.
Signed-off-by: NZhu Yanhai <gaoyang.zyh@taobao.com>
Acked-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/cgroups/memory.txt

@@ -61,7 +61,7 @@ Brief summary of control files.
  memory.failcnt			 # show the number of memory usage hits limits
  memory.memsw.failcnt		 # show the number of memory+Swap hits limits
  memory.max_usage_in_bytes	 # show max memory usage recorded
- memory.memsw.usage_in_bytes	 # show max memory+Swap usage recorded
+ memory.memsw.max_usage_in_bytes # show max memory+Swap usage recorded
  memory.soft_limit_in_bytes	 # set/show soft limit of memory usage
  memory.stat			 # show various statistics
  memory.use_hierarchy		 # set/show hierarchical account enabled