net: dsa: loop: Initialize err in dsa_loop_vlan_dump

Dan's static checker reported the following:

	drivers/net/dsa/dsa_loop.c:223 dsa_loop_port_vlan_dump()
	error: uninitialized symbol 'err'.

which could happen if we do hit the continue statement for each iteration of
the loop. Initialize err to 0 here.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 98cd1552 ("net: dsa: Mock-up driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/dsa_loop.c

@@ -194,7 +194,7 @@ static int dsa_loop_port_vlan_dump(struct dsa_switch *ds, int port,
 	struct mii_bus *bus = ps->bus;
 	struct dsa_loop_vlan *vl;
 	u16 vid, vid_start = 0;
-	int err;
+	int err = 0;
 
 	dev_dbg(ds->dev, "%s\n", __func__);