fix #29327388

commit 9b048119a153590b934ef49aae309b723587f527 upstream

nvme_init_iod should really be split into two parts: initialize a few
general iod fields, which can easily be done at the beginning of
nvme_queue_rq, and allocating the scatterlist if needed, which logically
belongs into nvme_map_data with the code making use of it.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NKeith Busch <keith.busch@intel.com>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>
Reviewed-by: NChaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: NBaolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>