The hashed-strings signature property includes two uint32_t values.
The first is unneeded as there should never be a start offset into the
strings region. The second, the size, is needed because the added
signature node appends to this region.
See tools/image-host.c, where a static 0 value is used for the offset.
Signed-off-by: Teddy Reed <teddy.reed@gmail.com> Reviewed-by: Simon Glass <sjg@chromium.org>