[ALSA] ad1848: fix AD1848P macro

Consistent variable naming is a good thing, but let's be a little less
sneaky about enforcing it... ;-/

Signed-off-by: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>