Allow opening the dedicated SPDIF stream while running on analog dup
mode.  Then the SPDIF stream is once reset and assigned for the new
stream.  It's useful for exclusive SPDIF output like AC3/DTS.
(In the former version, you had to close once the analog stream to
 play the exclusive digital stream.)
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>