mm/memory-failure: refactor log format in unpoison_memory

mm/memory-failure: refactor log format in unpoison_memory

Logs from memory_failure and other memory-failure.c code follow the
format:

  "Memory failure: 0x{pfn}: ${lower_case_message}"

Convert the logs in unpoison_memory to follow similar format:

  "Unpoison: 0x${pfn}: ${lower_case_message}"

For example (from local test):
  [ 1331.938397] Unpoison: 0x144bc8: page was already unpoisoned

No functional change in this commit.

Link: https://lkml.kernel.org/r/20240619063355.171313-1-jiaqiyan@google.com
Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>