ALSA: aloop: Release cable upon open error path

ALSA: aloop: Release cable upon open error path

commit 9685347aa0a5c2869058ca6ab79fd8e93084a67f upstream.

The aloop runtime object and its assignment in the cable are left even
when opening a substream fails.  This doesn't mean any memory leak,
but it still keeps the invalid pointer that may be referred by the
another side of the cable spontaneously, which is a potential Oops
cause.

Clean up the cable assignment and the empty cable upon the error path
properly.

Fixes: 597603d615d2 ("ALSA: introduce the snd-aloop module for the PCM loopback")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>