io_uring: don't do async setup for links' heads

Now, as we can do async setup without holding an SQE, we can skip doing
io_req_defer_prep() for link heads, it will be tried to be executed
inline and follows all the rules of the non-linked requests.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -6820,9 +6820,6 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 			ctx->drain_next = 0;
 		}
 		if (req->flags & (REQ_F_LINK | REQ_F_HARDLINK)) {
-			ret = io_req_defer_prep(req);
-			if (unlikely(ret))
-				req->flags |= REQ_F_FAIL_LINK;
 			link->head = req;
 			link->last = req;
 		} else {