Documentation/vm/transhuge.txt: fix trivial typos

[akpm@linux-foundation.org: fixes per Randy]
Link: http://lkml.kernel.org/r/20170405210259.2067-1-sj38.park@gmail.com


Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>