md/raid10: improve code of mrdev in raid10_sync_request

commit 59f8f0b54c8ffb4521f6bbd1cb6f4dfa5022e75e upstream.

'need_recover' and 'mrdev' are equivalent in raid10_sync_request(), and
inc mrdev->nr_pending is unreasonable if don't need recovery. Replace
'need_recover' with 'mrdev', and only inc nr_pending when needed.

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230527072218.2365857-3-linan666@huaweicloud.com


Cc: Hagar Gamal Halim <hagarhem@amazon.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>