media: MAINTAINERS: Add myself to iris Reviewers

There's some crossover between venus and iris, I'd like to help out with
the reviews for iris to ensure we keep upstream chugging along.

Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>