MAINTAINERS: update media vimc driver maintainers

Based on the dicussion with Hans Verkuil and others in the thread below,
vimc is need of a maintainer. I will start maintaining the driver with
help from Kieran Bingham as the reviewer.

Link: https://lore.kernel.org/linux-media/5d5dee88-9dbf-e4d0-4a91-11ff4ecd82ea@xs4all.nl/


Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Helen Koike <helen@koikeco.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>