[ALSA] sound: fix PCM substream list

If snd_pcm_new_stream() fails to initalize a substream (if
snd_pcm_substream_proc_init() returns error), snd_pcm_new_stream()
immediately return without unlinking that kfree()d substram.
It causes oops when snd_pcm_free() iterates the list of substream to
free them by invalid reference.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>