net: mscc: ocelot: fix memory leak on ocelot_port_add_txtstamp_skb()

If ocelot_port_add_txtstamp_skb() fails, for example due to a full PTP
timestamp FIFO, we must undo the skb_clone_sk() call with kfree_skb().
Otherwise, the reference to the skb clone is lost.

Fixes: 52849bc ("net: mscc: ocelot: avoid overflowing the PTP timestamp FIFO")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20241205145519.1236778-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: vladimiroltean

drivers/net/ethernet/mscc/ocelot_ptp.c

@@ -688,8 +688,10 @@ int ocelot_port_txtstamp_request(struct ocelot *ocelot, int port,
 			return -ENOMEM;
 
 		err = ocelot_port_add_txtstamp_skb(ocelot, port, *clone);
-		if (err)
+		if (err) {
+			kfree_skb(*clone);
 			return err;
+		}
 
 		OCELOT_SKB_CB(skb)->ptp_cmd = ptp_cmd;
 		OCELOT_SKB_CB(*clone)->ptp_class = ptp_class;