MAINTAINERS: Add James as MIPS co-maintainer

MAINTAINERS: Add James as MIPS co-maintainer

I've been taking on some co-maintainer duties already, so lets make it
official in the MAINTAINERS file.

Link: https://lkml.kernel.org/r/33db77a2-32e4-6b2c-d463-9d116ba55623@imgtec.com
Link: https://lkml.kernel.org/r/20171207110549.GM27409@jhogan-linux.mipstec.com
Signed-off-by: James Hogan <jhogan@kernel.org>
Acked-by: Paul Burton <paul.burton@mips.com>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: David Daney <david.daney@cavium.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: John Crispin <john@phrozen.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18211/