scd: Fix PK_AUTH with --challenge-response option.
* scd/app.c (app_auth): It's only APPTYPE_OPENPGP which supports the challenge response interaction. * scd/command.c (cmd_pkauth): It only wants if it works or not.
- GnuPG-bug-id: T5862
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>