usb: r8a66597-hcd: use platform_{get,set}_drvdata()

Use the wrapper functions for getting and setting the driver data using
platform_device instead of using dev_{get,set}_drvdata() with &of->dev,
so we can directly pass a struct platform_device.

Signed-off-by: Libo Chen <libo.chen@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>