image: Use ENOENT instead of ENOMEDIUM for better compatibility

This error may not be defined on some platforms such as MacOS so host
compilation will fail. Use one of the more common errors instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Andreas Bießmann <andreas.devel@googlemail.com>
Tested-by: Lubomir Popov <lpopov@mm-sol.com>
Merge branch 'master' of git://git.denx.de/u-boot into sunxi-current