irqchip: fix typo when moving gic_raise_softirq()

In b1cffebf (ARM: GIC: remove direct use of gic_raise_softirq)
gic_raise_softirq() was moved inside arch/arm/common/gic.c but in the
process it reverted by mistake a change to that function made by
384a2902

 (ARM: gic: use a private mapping for CPU target interfaces).
This breaks multicluster systems on ARM.

This patch fixes the typo.

Signed-off-by: Javi Merino <javi.merino@arm.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Olof Johansson <olof@lixom.net>