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

Fixes: 96868dce ("gpio/sifive: Add GPIO driver for SiFive SoCs")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>