ALSA: usb: stream: fix potential memory leak during uac3 interface parsing

UAC3 channel map is created during interface parsing,
and in some cases was not freed in failure paths.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>