irqchip/apple-aic: Fix refcount leak in build_fiq_affinity

of_find_node_by_phandle() returns a node pointer with refcount
incremented, we should use of_node_put() on it when not need anymore.
Add missing of_node_put() to avoid refcount leak.

Fixes: a5e88012 ("irqchip/apple-aic: Parse FIQ affinities from device-tree")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220601080930.31005-3-linmq006@gmail.com