ALSA: asihpi: fix spellint typo in comments

Change the comment typo: "ununsed" -> "unused".

Signed-off-by: Wang Qing <wangqing@vivo.com>
Link: https://lore.kernel.org/r/1600329372-2266-1-git-send-email-wangqing@vivo.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>