It is possible for blkg creation to fail when in blk_get_rl(). In this
situation, the fallback logic returns the nearest created blkg. There is
however special handling for the request_list for the root blkcg. This
fixes the missing edge case from the earlier series changing
blk_get_rl().

Fixes: e2b09899 ("blkcg: cleanup and make blk_get_rl use blkg_lookup_create")
Signed-off-by: NDennis Zhou <dennis@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>