fdtdec: fix OF_CONTROL switch

There is no case where defined(SPL_DISABLE_OF_CONTROL) is true.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>