ALSA: firewire-lib: code refactoring for selection of IT context header length

This commit refactors regarding to the size of CIP header.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210520040154.80450-4-o-takashi@sakamocchi.jp


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