powerpc/powermac/pfunc_base: Add missing of_node_put() in macio_gpio_init_one()

Call of_node_put() for the reference 'gparent' escaped out of the
previous for_each_child_of_node() as it has increased the refcount.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220716073111.539739-1-windhl@126.com