gpg: Fix AEAD preference list overflow

* g10/getkey.c (fixup_uidnode): Increase size of prefs array.

which introduced a feature to show the AEAD preferences of keys
created with rfc4880bis capable software (e.g. GnuPG 2.3-beta).
The same code in 2.3 is correct, though.

• GnuPG-bug-id: T5050
• Fixes-commit: ab7a0b07024c432233e691b5e4be7e32baf8d80f
• Signed-off-by: Werner Koch <wk@gnupg.org>