scd: Fix reading of the ATR for card type detection.

* scd/app.c (app_new_register): Do not use apdu_get_slot.

apdu_get_slot() may only be used after the APP has been initialized.
Thus we need to pass teh slot here directly.

• Fixes-commit: 9f148360a2bf04672b43ef7cec48e21d44b06ae1
• Signed-off-by: Werner Koch <wk@gnupg.org>