phylink: make local function phylink_phy_change() static

Fixes the following sparse warnings:

drivers/net/phy/phylink.c:570:6: warning:
 symbol 'phylink_phy_change' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/phy/phylink.c

@@ -567,7 +567,8 @@ void phylink_destroy(struct phylink *pl)
 }
 EXPORT_SYMBOL_GPL(phylink_destroy);
 
-void phylink_phy_change(struct phy_device *phydev, bool up, bool do_carrier)
+static void phylink_phy_change(struct phy_device *phydev, bool up,
+			       bool do_carrier)
 {
 	struct phylink *pl = phydev->phylink;