io_uring: inline io_iter_do_read()

There are only two calls in source code of io_iter_do_read(), the
function is small and pretty hot though is failed to get inlined.
Makr it as inline.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/25a26dae7660da73fbc2244b361b397ef43d3caf.1623634182.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -3253,7 +3253,7 @@ static bool io_rw_should_retry(struct io_kiocb *req)
 	return true;
 }
 
-static int io_iter_do_read(struct io_kiocb *req, struct iov_iter *iter)
+static inline int io_iter_do_read(struct io_kiocb *req, struct iov_iter *iter)
 {
 	if (req->file->f_op->read_iter)
 		return call_read_iter(req->file, &req->rw.kiocb, iter);