dtoc: Fix widening an int array to an int

An int array can hold a single int so we should not need to do anything
in the widening operation. However due to a quirk in the code, an int[3]
widened with an int produced an int[4]. Fix this and add a test.

Fix a comment typo while we are here.

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