MAINTAINERS: update Naoya Horiguchi's email address

My old NEC address has been removed, so update MAINTAINERS and .mailmap to
map it to my gmail address.

Link: https://lkml.kernel.org/r/20240412181720.18452-1-nao.horiguchi@gmail.com
Signed-off-by: Naoya Horiguchi <nao.horiguchi@gmail.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>