Fix double free of zone cache data

Fix double free of zone cache data

We can't set it up in the parsing callback, as that happens before
we fork off the thread. Fixes a segfault with:

./fio --ioengine=libaio --randrepeat=0 --norandommap --thread --direct=1 --name=pre_test --rw=randwrite --bssplit=4k/67:8k/10:16k/7:32k/3:64k/13 --random_distribution=zoned:50/5:30/15:20/80 --iodepth=32 --runtime=60 --time_based --numjobs=2 --filename=/dev/nvme0n1p9 --group_reporting=1

Fixes: https://github.com/axboe/fio/issues/650
Fixes: e0a04ac15f61 ("Add support for zones of random IO, with varying frequency of access")
Signed-off-by: Jens Axboe <axboe@kernel.dk>