s390/qeth: clean up a magic number in the OAT callback

Use the correct struct member instead of hardcoding its offset.
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_core_main.c

@@ -4839,7 +4839,6 @@ static int qeth_setadpparms_query_oat_cb(struct qeth_card *card,
 {
 	struct qeth_ipa_cmd *cmd = (struct qeth_ipa_cmd *)data;
 	struct qeth_qoat_priv *priv;
-	char *resdata;
 	int resdatalen;
 
 	QETH_CARD_TEXT(card, 3, "qoatcb");
@@ -4848,13 +4847,12 @@ static int qeth_setadpparms_query_oat_cb(struct qeth_card *card,
 
 	priv = (struct qeth_qoat_priv *)reply->param;
 	resdatalen = cmd->data.setadapterparms.hdr.cmdlength;
-	resdata = (char *)data + 28;
 
 	if (resdatalen > (priv->buffer_len - priv->response_len))
 		return -ENOSPC;
 
-	memcpy((priv->buffer + priv->response_len), resdata,
-		resdatalen);
+	memcpy(priv->buffer + priv->response_len,
+	       &cmd->data.setadapterparms.hdr, resdatalen);
 	priv->response_len += resdatalen;
 
 	if (cmd->data.setadapterparms.hdr.seq_no <