[ACPI] acpi_memhotplug.c build fix

drivers/acpi/acpi_memhotplug.c: In function `acpi_memory_get_device_resources':
drivers/acpi/acpi_memhotplug.c:101: error: structure has no member named `attribute'
drivers/acpi/acpi_memhotplug.c:103: error: structure has no member named `attribute'
drivers/acpi/acpi_memhotplug.c: In function `acpi_memory_disable_device':
drivers/acpi/acpi_memhotplug.c:253: warning: unused variable `attr'

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>