ALSA: firewire-motu: code refactoring for packet format detection in v2 protocol

Current implementation of driver has several similar helper functions
for packet format detection in protocol version 2.

This commit merges them as code refactoring.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210623075941.72562-6-o-takashi@sakamocchi.jp


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