MIPS: OCTEON: cvmx_mio_fus_dat3: use oldest forward compatible definition

Chips up to cn5xxx are compatible with cn38xx. All cn6xxx chips, and also
cnf71xx, are compatible with cn61xx.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
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