ALSA: opti93x - Fix NULL dereference

Probing non-existing device causes Oops with snd-opti93x driver
due to NULL access in the destructor of the error path.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Rene Herman <rene.herman@gmail.com>
Acked-by: Rene Herman <rene.herman@gmail.com>
Tested-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Ingo Molnar <mingo@elte.hu>