ACPI: glue: Use acpi_device_adr() in acpi_find_child_device()

Instead of evaluating _ADR in acpi_find_child_device(), use the
observation that it has already been evaluated and the value returned
by it has been stored in the pnp.type.bus_address field of the ACPI
device object at hand.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>