bus: hisi_lpc: Use platform_device_register_full()

The code to create the child platform device is essentially the same as
what platform_device_register_full() does, so change over to use
that same function to reduce duplication.

Signed-off-by: John Garry <john.garry@huawei.com>
Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>