pmdomain: qcom-cpr: Use helper function for_each_available_child_of_node()

pmdomain: qcom-cpr: Use helper function for_each_available_child_of_node()

for_each_available_child_of_node() can help to iterate through the
device_node, and we don't need to use while loop. Besides, the purpose
of the while loop is to find a device_node which fits the condition
"child_req_np == ref_np", we can just read the property of "child_np"
directly in for_each_available_child_of_node(). No functional change
with such conversion.

Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>
Link: https://lore.kernel.org/r/20240821034022.27394-2-zhangzekun11@huawei.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>