nvme-fc: avoid gcc-10 zero-length-bounds warning

When CONFIG_ARCH_NO_SG_CHAIN is set, op->sgl[0] cannot be dereferenced,
as gcc-10 now points out:

drivers/nvme/host/fc.c: In function 'nvme_fc_init_request':
drivers/nvme/host/fc.c:1774:29: warning: array subscript 0 is outside the bounds of an interior zero-length array 'struct scatterlist[0]' [-Wzero-length-bounds]
 1774 |  op->op.fcp_req.first_sgl = &op->sgl[0];
      |                             ^~~~~~~~~~~
drivers/nvme/host/fc.c:98:21: note: while referencing 'sgl'
   98 |  struct scatterlist sgl[NVME_INLINE_SG_CNT];
      |                     ^~~

I don't know if this is a legitimate warning or a false-positive.
If this is just a false alarm, the warning is easily suppressed
by interpreting the array as a pointer.

Fixes: b1ae1a23 ("nvme-fc: Avoid preallocating big SGL for data")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/fc.c

@@ -2106,7 +2106,7 @@ nvme_fc_init_request(struct blk_mq_tag_set *set, struct request *rq,
 	res = __nvme_fc_init_request(ctrl, queue, &op->op, rq, queue->rqcnt++);
 	if (res)
 		return res;
-	op->op.fcp_req.first_sgl = &op->sgl[0];
+	op->op.fcp_req.first_sgl = op->sgl;
 	op->op.fcp_req.private = &op->priv[0];
 	nvme_req(rq)->ctrl = &ctrl->ctrl;
 	return res;