x86: tnc: Change disable_igd() to have a return value

So far disable_igd() does not have any return value, but we may need
that in the future.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
1 file changed