ALSA: firewire-motu: parse messages for mixer output parameters in register DSP model

This commit parses message and cache current parameters of mixer output
function, commonly available for all of register DSP model

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20211015080826.34847-6-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>