ALSA: dice: fix compiler warning due to returning uninitialized value

This commit fixes the warning due to returning uninitialized value
from start_streams() helper function.

   sound/firewire/dice/dice-stream.c: In function 'start_streams.isra.0':
>> sound/firewire/dice/dice-stream.c:350:6: warning: 'err' may be used uninitialized in this function [-Wmaybe-uninitialized]
     int err;
         ^~~

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 3cd2c2d7

 ("ALSA: dice: reserve/release isochronous resources in pcm.hw_params/hw_free callbacks")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>