ALSA: nm256: Replace the words blacklist

Follow the recent inclusive terminology guidelines and replace the
words "whitelist" and "blacklist" appropriately.

Only comment or enum/variable renames, no functional changes.

Link: https://lore.kernel.org/r/20200714172631.25371-9-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>