md: factor error handling out of md_done_sync into helper

md: factor error handling out of md_done_sync into helper

The 'ok' parameter in md_done_sync() is redundant for most callers that
always pass 'true'. Factor error handling logic into a separate helper
function md_sync_error() to eliminate unnecessary parameter passing and
improve code clarity.

No functional changes introduced.

Link: https://lore.kernel.org/linux-raid/20260105110300.1442509-3-linan666@huaweicloud.com
Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Yu Kuai <yukuai@fnnas.com>