ACPI: NFIT: Use kobj_to_dev() instead

Use kobj_to_dev() instead of container_of()

Signed-off-by: Wang Qing <wangqing@vivo.com>
Acked-by: Vishal Verma <vishal.l.verma@intel.com>
[ rjw: Subject edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>