ACPI: Use list_for_each_entry() in acpi_unbind_one()

Since acpi_unbind_one() walks physical_node_list under the ACPI
device object's physical_node_lock mutex and the walk may be
terminated as soon as the matching entry has been found, it is
not necessary to use list_for_each_safe() for that walk, so use
list_for_each_entry() instead and make the code slightly more
straightforward.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
Acked-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>