ALSA: firewire-lib: code refactoring for pool position in rx packets

When scheduling transmission of rx packets, current implementation
fulfils packet descriptors after pooling sequence descriptors. It is for
packet queueing. Besides the implementations do not necessarily have
good readability.

This commit refactors them by adding function local variables and
function arguments.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20230107023214.29132-3-o-takashi@sakamocchi.jp


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