imx-image: Correctly fill image size in prepended header
If called with '-b' option 'imx-image' tool prepends barebox header to
the image, but the tool does not fill the data at image size offset
correctly. Fix that.
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>