ACPI: dock: dock_add - hoist up platform_device_register_simple()

Move the call to platform_device_register_simple so that we do it
before allocating and initializing our struct dock_station.

Signed-off-by: Alex Chiang <achiang@hp.com>
Acked-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>