de2104x: wrong MAC address fix

The de2104x returns sometimes a wrong MAC address. The wrong one is
like the original one, but it comes with an one byte shift. I found
this bug on an older alpha ev5 cpu. More details are available in Gentoo
bugreport #240718.

It seems the hardware is sometimes a little bit too slow for an
immediate access. This patch solves the problem by introducing a small
udelay.

Signed-off-by: Martin Langer <martin-langer@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>