ALSA: firewire-motu: drop protocol structure

Now protocol structure becomes useless. This commit drops it.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20200519111641.123211-6-o-takashi@sakamocchi.jp


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