brcm63xx: fix missing antislash in BCM6345 ethernet patch

This would cause build failure when disabling support for particular
CPUs.

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

git-svn-id: svn://svn.openwrt.org/openwrt@36946 3c298f89-4303-0410-b956-a3cf2f4a3e73