[ALSA] sparc dbri comment fix

This is a comment fix to avoid misleading about locking in the
dbri_cmdsend.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>