nvme-pci: remove useless assignment in nvme_pci_setup_prps

If prp_list is NULL, nvme_unmap_sg will be performed, and the assignment
to first_dma is meaningless, so remove it.
Signed-off-by: Liu Song <liusong@linux.alibaba.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/pci.c

@@ -670,7 +670,6 @@ static blk_status_t nvme_pci_setup_prps(struct nvme_dev *dev,
 
 	prp_list = dma_pool_alloc(pool, GFP_ATOMIC, &prp_dma);
 	if (!prp_list) {
-		iod->first_dma = dma_addr;
 		iod->npages = -1;
 		return BLK_STS_RESOURCE;
 	}