thp: fix comments of __pmd_trans_huge_lock()

To make the comments consistent with the already changed code.

Link: http://lkml.kernel.org/r/1466200004-6196-1-git-send-email-ying.huang@intel.com


Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>