[ALSA] sparc dbri: SMP fixes

The dbri driver hangs when used in kernel compiled with SMP
support due to inproper locking. The patch fixes it.

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>