ALSA: hdspm: Fix typo arbitary

Fix comment typo.
s/arbitary/arbitrary/

Signed-off-by: Naoki Hayama <naoki.hayama@lineo.co.jp>
Link: https://lore.kernel.org/r/e04a8c5b-8c59-3f02-34d3-c1a871d08cc2@lineo.co.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>