[PATCH] fix extra page ref count in follow_hugetlb_page

git-commit: d5d4b0aa
"[PATCH] optimize follow_hugetlb_page" breaks mlock on hugepage areas.

I mis-interpret pages argument and made get_page() unconditional.  It
should only get a ref count when "pages" argument is non-null.

Credit goes to Adam Litke who spotted the bug.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Acked-by: Adam Litke <agl@us.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>