PCI: rpadlpar: Use for_each_child_of_node() and for_each_node_by_name()

Use for_each_child_of_node() and for_each_node_by_name() macros instead of
open coding them.

Link: https://lore.kernel.org/r/20200916062128.190819-1-miaoqinglang@huawei.com


Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>