km/scripts: fix saveenv command syntax

This is most probably a typo, and in older u-uboot versions is same as
'saveenv', in the newer uboot versions there is a separate 'save' command
that is different from 'saveenv'.

Signed-off-by: Aleksandar Gerasimovski <aleksandar.gerasimovski@hitachi-powergrids.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>