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>

Backport of r46200

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@46252 3c298f89-4303-0410-b956-a3cf2f4a3e73