irqchip/gic-v3: Always return IRQ_SET_MASK_OK_DONE in gic_set_affinity

Always return IRQ_SET_MASK_OK_DONE instead of IRQ_SET_MASK_OK when the
affinity has been updated. When using stacked irqchips, returning
IRQ_SET_MASK_OK_DONE means skipping all descendant irqchips.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>