ALSA: fireface: add helper function to parse MIDI messages transmitted by Fireface 400

This is minor code refactoring to add helper function to parse MIDI message
bytes in quadlet message.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20230112120954.500692-4-o-takashi@sakamocchi.jp


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