io_uring: remove extra SQPOLL overflow flush

c1edbf5 ("io_uring: flag SQPOLL busy condition to userspace")
added an extra overflowed CQE flush in the SQPOLL submission path due to
backpressure, which was later removed. Remove the flush and let
io_cqring_wait() / iopoll handle it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2a83b0724ca6ca9d16c7d79a51b77c81876b2e39.1712708261.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -3238,8 +3238,6 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 	 */
 	ret = 0;
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
-		io_cqring_overflow_flush(ctx);
-
 		if (unlikely(ctx->sq_data->thread == NULL)) {
 			ret = -EOWNERDEAD;
 			goto out;