hwpoison: fix hugetlbfs/thp precheck in hwpoison_user_mappings()

Recent fix from Chen Yucong (commit 0bc1f8b0682c "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 the mce-test testsuite
passes.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
hwpoison: call action_result() in failure path of hwpoison_user_mappings()

hwpoison_user_mappings() could fail for various reasons, so printk()s
to print out the reasons should be done in each failure check inside
hwpoison_user_mappings().
And currently we don't call action_result() when hwpoison_user_mappings()
fails, which is not consistent with other exit points of memory error
handler. So this patch fixes these messaging problems.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>