blk-cgroup: don't update the blkg lookup hint in blkg_conf_prep

blkg_conf_prep just creates a new blkg structure, there is no real
need to update the lookup hint which should only be done on a
successful lookup in the I/O path.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220927065425.257876-1-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>