lightnvm: unlock rq and free ppa_list on submission fail

When rrpc_write_ppalist_rq and rrpc_read_ppalist_rq succeed, we setup
rq correctly, but nvm_submit_io may afterward fail since it cannot
allocate request or nvme_nvm_command, we return error but forget to
cleanup the previous work.

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>