MIPS: cavium-octeon: fix out-of-bounds array access

When booting with in-kernel DTBs, the pruning code will enumerate
interfaces 0-4. However, there is memory reserved only for 4 so some
other data will get overwritten by cvmx_helper_interface_enumerate().

Signed-off-by: Aaro Koskinen <aaro.koskinen@nsn.com>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6102/