MIPS: OCTEON: fix out of bounds array access on CN68XX

The maximum number of interfaces is returned by
cvmx_helper_get_number_of_interfaces(), and the value is used to access
interface_port_count[]. When CN68XX support was added, we forgot
to increase the array size. Fix that.

Fixes: 2c8c3f02

 ("MIPS: Octeon: Support additional interfaces on CN68XX")
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20949/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # v4.3+