lightnvm: fix ioctl memory leaks

If copy_to_user() fails we returned error but we missed releasing
devices.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>