net/ll_temac: FIX : Wait for indirect wait to end

While tracing down a connectivity problem on the temac I connected a
probe to the Cross bar irq, and it was triggered when doing
ifdown->ifup.

This is fixed once waiting for the indirect write to end. Since it is
not on the hot path there is no performance loss.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>