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>