MIPS: OCTEON: cvmx_pko_mem_debug8: use oldest forward compatible definition

cn58xx is compatible with cn50xx, so use the latter.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
[paul.burton@mips.com: s/cn52xx/cn50xx/ in commit message.]
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org