ALSA: firewire-digi00x: prevent potential use after free

This code was supposed to return an error code if init_stream()
failed, but it instead freed dg00x->rx_stream and returned success.
This potentially leads to a use after free.

Fixes: 9a08067e

 ("ALSA: firewire-digi00x: support AMDTP domain")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/c224cbd5-d9e2-4cd4-9bcf-2138eb1d35c6@kili.mountain
Signed-off-by: Takashi Iwai <tiwai@suse.de>