cns3xxx: fix USB ehci/ohci platform driver

Update ehci/ohci driver registration to conform to the new platform
drivers.

This fixes missing USB host support in 3.8.x

Signed-off-by: Tim Harvey <tharvey@gateworks.com>

git-svn-id: svn://svn.openwrt.org/openwrt@36309 3c298f89-4303-0410-b956-a3cf2f4a3e73