MAINTAINERS: Add Rodger Combs to ffmpeg-security

Rodger Combs will be added to the ffmpeg-security alias when this patch is applied

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Reviewed-by: Clément Bœsch <u@pkh.me>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
