md/raid10: Fix typo in comment (replacment -> replacement)

Replace replacment with replacement.

Signed-off-by: Jiangshan Yi <yijiangshan@kylinos.cn>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230214064013.2373851-1-yijiangshan@kylinos.cn