scd: Fix flushing of CA-FPR data objects

* scd/app-openpgp.c (do_setattr): Add new table item to flush a
different tag.

For whatever reasons the OpenPGP card reads the 3 CA fingerprints from
one object but sets them individually using 3 different tags. The
cache flushing was not prepared for this and so a changed CA
fingerprint showed only up after a card reset. This patch fixes it.

• Signed-off-by: Werner Koch <wk@gnupg.org>