nvme-tcp: fix data digest pointer calculation

ddgst is of type __le32, &req->ddgst + req->offset
increases &req->ddgst by 4 * req->offset, fix this by
type casting &req->ddgst to u8 *.

Fixes: 3f2304f8 ("nvme-tcp: add NVMe over TCP host driver")
Signed-off-by: Varun Prakash <varun@chelsio.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/tcp.c

@@ -1054,7 +1054,7 @@ static int nvme_tcp_try_send_ddgst(struct nvme_tcp_request *req)
 	int ret;
 	struct msghdr msg = { .msg_flags = MSG_DONTWAIT };
 	struct kvec iov = {
-		.iov_base = &req->ddgst + req->offset,
+		.iov_base = (u8 *)&req->ddgst + req->offset,
 		.iov_len = NVME_TCP_DIGEST_LENGTH - req->offset
 	};