media: MAINTAINERS: camss: Add Robert Foss as co-maintainer

I would like to contribute some of my time to co-maintain the CAMSS
driver. I'm currently working to extend CAMSS to new hardware platforms.

Signed-off-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>