x86: itss: Tidy up bind() for of-platdata-inst

With the standard of-platdata we must fix up driver_data manually. With
of-platadata-inst this is not necessary, since it is added to the device
by dtoc.

Update the code to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>