scd: Add a workaround for Yubikey.

* scd/app-openpgp.c (get_public_key): Handle wrong code for Yubikey.

Backport master commit of:

0db9c83555b4a8a0c52f96e96ec20dbfd3d75272

Yubikey version 5 s/n 609074582 returns 0x6982, version 5.2.4 s/n
610616049 returns 0x6581, where 0x6a88 is expected.

• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>