lantiq: fix a regression in the eiu irq loading code

this worked in 3.18 but broke at some point. the old code that loaded a
irq table was incorrewct anyhow as it mapped the irqs int he domain which
should really be done when the driver using them loads them and not the
irq driver itself.

Signed-off-by: John Crispin <john@phrozen.org>