net: dsa: ocelot: fix "should it be static?" warnings

Fix following sparse warnings:
drivers/net/dsa/ocelot/felix.c:351:6: warning: symbol 'felix_txtstamp' was not declared. Should it be static?
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/ocelot/felix.c

@@ -348,8 +348,8 @@ static bool felix_rxtstamp(struct dsa_switch *ds, int port,
 	return false;
 }
 
-bool felix_txtstamp(struct dsa_switch *ds, int port,
-		    struct sk_buff *clone, unsigned int type)
+static bool felix_txtstamp(struct dsa_switch *ds, int port,
+			   struct sk_buff *clone, unsigned int type)
 {
 	struct ocelot *ocelot = ds->priv;
 	struct ocelot_port *ocelot_port = ocelot->ports[port];