clocksource/drivers/arm_arch_timer: Using for_each_available_child_of_node_scoped()

for_each_available_child_of_node_scoped() can put the device_node
automatically. So, using it to make the code logic more simple and
remove the device_node clean up code.

Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>
Link: https://lore.kernel.org/r/20240807074655.52157-1-zhangzekun11@huawei.com


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>