ALSA: firewire-lib: keep history to process isochronous packet

The history to process isochronous packets is useful when computing gap
between current isochronous cycle and the latest isochronous cycle in
which packet is processed (in IR context) and scheduled (in IT context).

This commit stores the most recent packet descriptors to keep the history.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20230109021738.75543-4-o-takashi@sakamocchi.jp


Signed-off-by: Takashi Iwai <tiwai@suse.de>