ACPI / PM: Fix /proc/acpi/wakeup for devices w/o bus or parent

Fix /proc/acpi/wakeup for devices without bus or parent

This patch fixes printing the wakeup status for devices without a bus
or parent, such as laptop lid switches and sleep buttons. These devices
have an empty physical_node_list, because acpi_bind_one is never run
for them.

[rjw: White space and coding style.]
Signed-off-by: Andreas Fleig <andreasfleig@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>