ALSA: firewire-lib: code refactoring for transfer delay

In later commit, transfer delay is used in both IR and IT contexts. This
commit refactors regardless of transfer delay.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210522013303.49596-7-o-takashi@sakamocchi.jp


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