mm/secretmem: add __init annotation to secretmem_init()

It's a fs_initcall entry, add __init annotation to it.

Link: https://lkml.kernel.org/r/20220915011602.176967-1-xiujianfeng@huawei.com


Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>