kbx: Increase size of field for fingerprint.

* kbx/keybox-search-desc.h (fpr): Increase the size.

In the function keydb_search_fpr in g10/keydb.c, it is copied using
MAX_FINGERPRINT_LEN. So, more size is required.

• Fixes-commit: ecbbafb88d920e713439b6b1b8e1b41a6f8d0e38
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>