scd:openpgp: Fix computing fingerprint for ECC with SOS.

* scd/app-openpgp.c (count_sos_bits): New.  Count as sos_write does.
(store_fpr): For ECC, use count_sos_bits.

(cherry picked from commit 95156ef9bfb6a3a525454d50ae2f5b538ccbd774)
and
(cherry picked from commit f482e4bd121ff2862bfb53a82f1d5c2cf3524a10)

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