imx: hab: Use size parameter

The current code works by sheer coincidence, because (see HABv4 API
documentation, section 3.4) the RVT authenticate_image call updates
the size that is passed in with the actual size ROM code pulls from
IVT/CSF . So if the input size is larger, that is "fine" . Pass in
size instead to make this really correct.

Signed-off-by: Marek Vasut <marex@denx.de>