env: Drop saveenv() in favour of env_save()

env: Drop saveenv() in favour of env_save()

Use the env_save() function directly now that there is only one
implementation of saveenv().

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Denk <wd@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>