net: phylink: avoid oops during initialisation

If we intend to use PCS operations, mac_pcs_get_state() will not be
implemented, so will be NULL. If we also intend to register the PCS
operations in mac_prepare() or mac_config(), then this leads to an
attempt to call NULL function pointer during phylink_start(). Avoid
this, but we must report the link is down.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phylink.c

@@ -535,8 +535,10 @@ static void phylink_mac_pcs_get_state(struct phylink *pl,
 
 	if (pl->pcs_ops)
 		pl->pcs_ops->pcs_get_state(pl->pcs, state);
-	else
+	else if (pl->mac_ops->mac_pcs_get_state)
 		pl->mac_ops->mac_pcs_get_state(pl->config, state);
+	else
+		state->link = 0;
 }
 
 /* The fixed state is... fixed except for the link state,