kdf: Prepare aligned memory in balloon_final.
* cipher/kdf.c (BALLOON_BLOCK_LEN_MAX): Rename from BALLOON_SALT_LEN_MAX. (balloon_xor_block): Revert the previous change. (balloon_final): Prepare memory for u64.
- GnuPG-bug-id: T5817
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>