asmc_key_getinfo() and asmc_key_dump_by_index() both ran the command 0x13
transaction, the latter after a command 0x12. Put each behind a helper that
assumes the caller holds sc_mtx, and fold the shared response decode into
asmc_keyinfo_decode().
The index bytes are now derived inside the helper, so they are recomputed
per retry. Same value all the time.