ALSA: firewire-lib: code refactoring for check of CIP header about payload size

The size of CIP payload is now passed to helper function to parse CIP
header.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210518130048.146596-7-o-takashi@sakamocchi.jp


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