net: dsa: check master device before put

In the case of pdata, the dsa_cpu_parse function calls dev_put() before
making sure it isn't NULL. Fix this.

Fixes: 71e0bbde ("net: dsa: Add support for platform data")
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/dsa2.c

@@ -496,13 +496,14 @@ static int dsa_cpu_parse(struct dsa_port *port, u32 index,
 		if (!ethernet)
 			return -EINVAL;
 		ethernet_dev = of_find_net_device_by_node(ethernet);
+		if (!ethernet_dev)
+			return -EPROBE_DEFER;
 	} else {
 		ethernet_dev = dsa_dev_to_net_device(ds->cd->netdev[index]);
-		dev_put(ethernet_dev);
-	}
-
 		if (!ethernet_dev)
 			return -EPROBE_DEFER;
+		dev_put(ethernet_dev);
+	}
 
 	if (!dst->cpu_dp) {
 		dst->cpu_dp = port;