ALSA: sb8: add a check for request_region

[ Upstream commit dcd0feac9bab901d5739de51b3f69840851f8919 ]

In case request_region fails, the fix returns an error code to
avoid NULL pointer dereference.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>