io_uring: remove index from sqe_submit

mainline inclusion
from mainline-5.5-rc1
commit fa456228
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27


CVE: NA
---------------------------

submit->index is used only for inbound check in submission path (i.e.
head < ctx->sq_entries). However, it always will be true, as
1. it's already validated by io_get_sqring()
2. ctx->sq_entries can't be changedd in between, because of held
ctx->uring_lock and ctx->refs.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: yangerkun <yangerkun@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>