brcm63xx: do not add twice the same field to board

Changeset r39302 updated a board section and added twice .has_ehci0,
this is not necessary, so fix it.

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

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39304 3c298f89-4303-0410-b956-a3cf2f4a3e73