When failing sound card registration after initializing stream data, this
module leaves allocated data in stream data. This commit fixes the bug.

Fixes: 9b2bb4f2 ('ALSA: firewire-motu: add stream management functionality')
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>