MAINTAINERS: Drop James Hogan as MIPS maintainer

I haven't been active for 18 months, and Paul seems to be doing a grand
job, so drop me from MIPS maintainership.

Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Paul Burton <paulburton@kernel.org>