scd: Fix compiler warnings for app-openpgp.c.
* scd/app-openpgp.c (retrieve_key_material): Remove touching I. (do_change_pin): Make sure going to leave if PINVALUE == 0. (rsa_writekey): Emit simpler log.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>