hwpoison: fix hugetlbfs/thp precheck in hwpoison_user_mappings()

A recent fix from Chen Yucong, commit 0bc1f8b0

 ("hwpoison: fix the
handling path of the victimized page frame that belong to non-LRU")
rejects going into unmapping operation for hugetlbfs/thp pages, which
results in failing error containing on such pages.  This patch fixes it.

With this patch, hwpoison functional tests in mce-test testsuite pass.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Chen Yucong <slaoub@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>