scd:openpgp: Fix PIN pin2hash_if_kdf.
* scd/app-openpgp.c (pin2hash_if_kdf): DEK had been changed to pointer to allocated memory, so, we need to use DEKLEN for the length.
- GnuPG-bug-id: T7121
- Fixes-commit: 20e85585ed20af67ce68e637ea5c3637615ba2e9
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>