ALSA: firewire-lib: code refactoring for generation of packet descriptors

This commit refactors the arguments of helper function to generate the
descriptors of packet.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210522013303.49596-4-o-takashi@sakamocchi.jp


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