scd: Skip unknown options in command SERIALNO

* scd/command.c (cmd_serialno): Skip options.

SERIALNO --all
works only in 2.3 and thus naive use with 2.2 vesions would conserer
"--all" as the reqyested applications. Fix is easy and should be done
anyway.

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