ALSA: oxfw: add an comment to Kconfig for TASCAM FireOne

A commit to add support for this model should have added a comment
about this model to Kconfig.

Fixes: 759a2f40('ALSA: oxfw: add an entry for TASCAM FireOne')
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>