io_uring: don't re-setup vecs/iter in io_resumit_prep() is already there

mainline inclusion
from mainline-v5.9-rc7
commit 8f3d7496
category: bugfix
bugzilla: 186136, https://gitee.com/openeuler/kernel/issues/I4RM1D


CVE: NA

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If we already have mapped the necessary data for retry, then don't set
it up again. It's a pointless operation, and we leak the iovec if it's
a large (non-stack) vec.

Fixes: b63534c4 ("io_uring: re-issue block requests that failed because of resources")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
conflict:
        fs/io_uring.c
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>