usb: dwc3: use local copy of resource to fix-up register offset

It is not a good idea to directly modify the resource of a platform
device.  Modify its local copy, and pass it to devm_ioremap_resource()
so that we do not need to restore it in the failure path and the remove
hook.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>