This saves one memory allocation, and ensures the bvecs aren't freed
before the AIO completion.  This will allow the lower level code to be
optimized so that it can avoid allocating another bvec array.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>