net: gianfar: fix device leak when querying time stamp info

Make sure to drop the reference to the ptp device taken by
of_find_device_by_node() when querying the time stamping capabilities.

Note that holding a reference to the ptp device does not prevent its
driver data from going away.

Fixes: 7349a74 ("net: ethernet: gianfar_ethtool: get phc index through drvdata")
Cc: [email protected]	# 4.18
Cc: Yangbo Lu <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: jhovold

drivers/net/ethernet/freescale/gianfar_ethtool.c

@@ -1475,8 +1475,10 @@ static int gfar_get_ts_info(struct net_device *dev,
 	if (ptp_node) {
 		ptp_dev = of_find_device_by_node(ptp_node);
 		of_node_put(ptp_node);
-		if (ptp_dev)
+		if (ptp_dev) {
 			ptp = platform_get_drvdata(ptp_dev);
+			put_device(&ptp_dev->dev);
+		}
 	}
 
 	if (ptp)