devlink: fix return value check in devlink_dpipe_header_put()

Fix the return value check which testing the wrong variable
in devlink_dpipe_header_put().

Fixes: 1555d204e743 ("devlink: Support for pipeline debug (dpipe)")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/devlink.c b/net/core/devlink.c
index 24b7660..0afac58 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -2031,7 +2031,7 @@
 	int err;
 
 	header_attr = nla_nest_start(skb, DEVLINK_ATTR_DPIPE_HEADER);
-	if (!header)
+	if (!header_attr)
 		return -EMSGSIZE;
 
 	if (nla_put_string(skb, DEVLINK_ATTR_DPIPE_HEADER_NAME, header->name) ||