MAINTAINERS: add dma-fence* files to Sync File maintainership

As Sync File is highly dependent on dma-fence* tracks it
under SYNC FILE_FRAMEWORK as well.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170127175444.7995-1-gustavo@padovan.org