dtoc: Correct the type widening code in fdt_fallback

This code does not match the fdt version in fdt.py. When dtoc is unable to
use the Python libfdt library, it uses the fallback version, which does not
widen arrays correctly.

Fix this to avoid a warning 'excess elements in array initialize' in
dt-platdata.c which happens on some platforms.

Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Tom Rini <trini@konsulko.com>