[ALSA] Fix typo and add entry to documentation

This patch adds the macpro and fixes a typo in the ALC882 section of
ALSA-Configuration.txt.

Signed-off-by: Tobin Davis <tdavis@dsl-only.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>