commit daa5de5415849b9a53056ec1e1e88fe4c5c9aa2b upstream.

After 75b28af("io_uring: allocate the two rings together"), we compare
sq.head with cached_cq_tail to determine does there any cq invalid.
Actually, we should use cq.head.

Fixes: 75b28affdd6a ("io_uring: allocate the two rings together")
Signed-off-by: Nyangerkun <yangerkun@huawei.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>