[Helix] pvr-addons: fix the mime type for mpegts

The changes from this PR are needed to prevent streaming problems for multiple pvr-addons when https://github.com/xbmc/xbmc/pull/6036 is merged.

See also https://github.com/FFmpeg/FFmpeg/commit/fdcb2873e1c898cf26216f7e80d95d03387ba55b for the related ffmpeg change.