This patch is from memory hotplug tree in lhms.
This patch changes memory_device's phys_device member from just a number
to symbolic link to the device. AFAIK, phys_device is not used now.

example)
$readlink /sys/devices/system/memory/memory10/phys_device
../../../../firmware/acpi/namespace/ACPI/_SB/LSB1/MEM3

This will help memory hotplug shell script.

-- Kame