md/raid10: fix memleak for 'conf->bio_split'

[ Upstream commit c9ac2acde53f5385de185bccf6aaa91cf9ac1541 ]

In the error path of raid10_run(), 'conf' need be freed, however,
'conf->bio_split' is missed and memory will be leaked.

Since there are 3 places to free 'conf', factor out a helper to fix the
problem.

Fixes: fc9977dd ("md/raid10: simplify the splitting of requests.")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230310073855.1337560-6-yukuai1@huaweicloud.com


Signed-off-by: Sasha Levin <sashal@kernel.org>