nvme: fix sqhd reference when admin queue connect fails

Fix bug in sqhd patch.

It wasn't the sq that was at risk. In the case where the admin queue
connect command fails, the sq->size field is not set. Therefore, this
becomes a divide by zero error.

Add a quick check to bypass under this failure condition.
Signed-off-by: NJames Smart <james.smart@broadcom.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/nvme/target/core.c

@@ -390,6 +390,7 @@ static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
 	if (status)
 		nvmet_set_status(req, status);
 
+	if (req->sq->size)
 		req->sq->sqhd = (req->sq->sqhd + 1) % req->sq->size;
 	req->rsp->sq_head = cpu_to_le16(req->sq->sqhd);
 	req->rsp->sq_id = cpu_to_le16(req->sq->qid);