net: dsa: b53: allow lower MTUs on BCM5325/5365

While BCM5325/5365 do not support jumbo frames, they do support slightly
oversized frames, so do not error out if requesting a supported MTU for
them.

Fixes: 6ae5834b ("net: dsa: b53: add MTU configuration support")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/dsa/b53/b53_common.c

@@ -2258,7 +2258,7 @@ static int b53_change_mtu(struct dsa_switch *ds, int port, int mtu)
 	bool allow_10_100;
 
 	if (is5325(dev) || is5365(dev))
-		return -EOPNOTSUPP;
+		return 0;
 
 	if (!dsa_is_cpu_port(ds, port))
 		return 0;