phy: mark lan88xx_suspend() static

We get 1 warning when building kernel with W=1:
drivers/net/phy/microchip.c:58:5: warning: no previous prototype for 'lan88xx_suspend' [-Wmissing-prototypes]

In fact, this function is only used in the file in which it is
declared and don't need a declaration, but can be made static.
so this patch marks this function with 'static'.
Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/microchip.c

@@ -55,7 +55,7 @@ static int lan88xx_phy_ack_interrupt(struct phy_device *phydev)
 	return rc < 0 ? rc : 0;
 }
 
-int lan88xx_suspend(struct phy_device *phydev)
+static int lan88xx_suspend(struct phy_device *phydev)
 {
 	struct lan88xx_priv *priv = phydev->priv;