media: MAINTAINERS: Add an entry for V4L2 sensor and lens drivers

I maintain V4L2 sensor and lens drivers but there hasn't been a specific
MAINTAINERS entry for them. Add it now.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>