usb: dwc3: remove unnecessary platform_set_drvdata()

Remove unnecessary platform_set_drvdata(..., NULL) in ->remove(),
the driver_data will be cleared in device_unbind_cleanup() after
calling ->remove() in driver call code.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/20230810134710.114356-1-yangyingliang@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>