scd:openpgp: Fix writing ECC key to card.
* scd/app-openpgp.c (build_privkey_template): Adding another argument of ecc_d_fixed_len to handle variable-size MPI.
Backport from master commit of:
a25c99b156ca9acaa7712e9c09a6df0a7a23c833
- GnuPG-bug-id: T5163
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>