ALSA: dice: fix memory leak when unplugging

When sound card is going to be released, dice private data is
also released. Then all of data should be released. However,
stream data is not released. This causes memory leak when
unplugging dice unit.

This commit fixes the bug.

Fixes: 4bdc495c('ALSA: dice: handle several PCM substreams when any isochronous streams are available')
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>