net: ibm: remove set but not used variables 'err'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/ibm/emac/core.c: In function __emac_mdio_write:
drivers/net/ethernet/ibm/emac/core.c:875:9: warning:
	variable err set but not used [-Wunused-but-set-variable]
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ibm/emac/core.c

@@ -872,7 +872,7 @@ static void __emac_mdio_write(struct emac_instance *dev, u8 id, u8 reg,
 {
 	struct emac_regs __iomem *p = dev->emacp;
 	u32 r = 0;
-	int n, err = -ETIMEDOUT;
+	int n;
 
 	mutex_lock(&dev->mdio_lock);
 
@@ -919,7 +919,6 @@ static void __emac_mdio_write(struct emac_instance *dev, u8 id, u8 reg,
 			goto bail;
 		}
 	}
-	err = 0;
  bail:
 	if (emac_has_feature(dev, EMAC_FTR_HAS_RGMII))
 		rgmii_put_mdio(dev->rgmii_dev, dev->rgmii_port);