lightnvm: fix bio submission issue

Put bio when submission fails, since we get it
before submission. And return error when backend
device driver doesn't provide a submit_io method,
thus we can end IO properly.

Signed-off-by: Wenwei Tao <ww.tao0320@gmail.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>