ar71xx: fix kernel Oops in at803x_link_change_notify

r45954 ("ar71xx: fix 100/10mbps ethernet link issues on mynet range
extender") introduced a pdata based modification of the tx_clk_dly. But it
was not checked if pdata actually existed. This caused a page fault on all
devices which didn't have at803x_platform_data specified for an at803x
based device.

Signed-off-by: Sven Eckelmann <sven@open-mesh.com>

SVN-Revision: 46200

target/linux/ar71xx/patches-3.18/425-net-phy-at803x-allow-to-configure-via-pdata.patch

@@ -141,7 +141,7 @@
  			priv->phy_reset = false;
  		}
  	}
-+	if (pdata->fixup_rgmii_tx_delay &&
++	if (pdata && pdata->fixup_rgmii_tx_delay &&
 +	    phydev->speed != priv->prev_speed) {
 +		switch (phydev->speed) {
 +		case SPEED_10: