adm8668: revert changeset 34554

The conversion was not 100% correct and leads to u-boot failing to
verify the CRC, revert that change for now.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42170 3c298f89-4303-0410-b956-a3cf2f4a3e73