net: dsa: convert dsa_user_phylink_fixed_state() to use dsa_phylink_to_port()

Convert dsa_user_phylink_fixed_state() to use the newly introduced
dsa_phylink_to_port() helper.
Suggested-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/user.c

@@ -2445,7 +2445,7 @@ EXPORT_SYMBOL_GPL(dsa_port_phylink_mac_change);
 static void dsa_user_phylink_fixed_state(struct phylink_config *config,
 					 struct phylink_link_state *state)
 {
-	struct dsa_port *dp = container_of(config, struct dsa_port, pl_config);
+	struct dsa_port *dp = dsa_phylink_to_port(config);
 	struct dsa_switch *ds = dp->ds;
 
 	/* No need to check that this operation is valid, the callback would