io-wq: fix max-workers not correctly set on multi-node system

In io-wq.c:io_wq_max_workers(), new_count[] was changed right after each
node's value was set. This caused the following node getting the setting
of the previous one.

Returned values are copied from node 0.

Fixes: 2e480058 ("io-wq: provide a way to limit max number of workers")
Signed-off-by: Beld Zhang <beldzhang@gmail.com>
[axboe: minor fixups]
Signed-off-by: Jens Axboe <axboe@kernel.dk>