plca.c: fix obvious mistake in checking retval

Revert a wrong fix that was done during the review process. The
intention was to substitute "if(ret < 0)" with "if(ret)".
Unfortunately, the intended fix did not meet the code.
Besides, after additional review, it was decided that "if(ret < 0)"
was actually the right thing to do.

Fixes: 8580e16c ("net/ethtool: add netlink interface for the PLCA RS")
Signed-off-by: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/f2277af8951a51cfee2fb905af8d7a812b7beaf4.1673616357.git.piergiorgio.beruto@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ethtool/plca.c

@@ -61,7 +61,7 @@ static int plca_get_cfg_prepare_data(const struct ethnl_req_info *req_base,
 	}
 
 	ret = ethnl_ops_begin(dev);
-	if (!ret)
+	if (ret < 0)
 		goto out;
 
 	memset(&data->plca_cfg, 0xff,
@@ -151,7 +151,7 @@ int ethnl_set_plca_cfg(struct sk_buff *skb, struct genl_info *info)
 					 tb[ETHTOOL_A_PLCA_HEADER],
 					 genl_info_net(info), info->extack,
 					 true);
-	if (!ret)
+	if (ret < 0)
 		return ret;
 
 	dev = req_info.dev;
@@ -171,7 +171,7 @@ int ethnl_set_plca_cfg(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	ret = ethnl_ops_begin(dev);
-	if (!ret)
+	if (ret < 0)
 		goto out_rtnl;
 
 	memset(&plca_cfg, 0xff, sizeof(plca_cfg));
@@ -189,7 +189,7 @@ int ethnl_set_plca_cfg(struct sk_buff *skb, struct genl_info *info)
 		goto out_ops;
 
 	ret = ops->set_plca_cfg(dev->phydev, &plca_cfg, info->extack);
-	if (!ret)
+	if (ret < 0)
 		goto out_ops;
 
 	ethtool_notify(dev, ETHTOOL_MSG_PLCA_NTF, NULL);
@@ -233,7 +233,7 @@ static int plca_get_status_prepare_data(const struct ethnl_req_info *req_base,
 	}
 
 	ret = ethnl_ops_begin(dev);
-	if (!ret)
+	if (ret < 0)
 		goto out;
 
 	memset(&data->plca_st, 0xff,