io_uring: simplify io_uring_cmd return

We don't have to return error code from an op handler back to core
io_uring, so once io_uring_cmd() sets the results and handles errors we
can juts return IOU_OK and simplify the code.

Note, only valid with e0b23d9 ("io_uring: optimise ltimeout for
inline execution"), there was a problem with iopoll before.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8eae2be5b2a49236cd5f1dadbd1aa5730e9e2d4f.1721819383.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/uring_cmd.c

@@ -265,7 +265,7 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 		req_set_fail(req);
 	io_req_uring_cleanup(req, issue_flags);
 	io_req_set_res(req, ret, 0);
-	return ret < 0 ? ret : IOU_OK;
+	return IOU_OK;
 }
 
 int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,