imx: image-container: Fix container header checking

Checking container header tag and version is wrong, it causes to fail
to bypass invalid container

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>