media: tw686x: Fix memory leak in tw686x_video_init

video_device_alloc() allocates memory for vdev,
when video_register_device() fails, it doesn't release the memory and
leads to memory leak, call video_device_release() to fix this.

Fixes: 704a84cc ("[media] media: Support Intersil/Techwell TW686x-based video capture cards")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>