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

MAINTAINERS

@@ -3976,6 +3976,7 @@ S:	Maintained
 L:	linux-media@vger.kernel.org
 L:	dri-devel@lists.freedesktop.org
 F:	drivers/dma-buf/sync_*
+F:	drivers/dma-buf/dma-fence*
 F:	drivers/dma-buf/sw_sync.c
 F:	include/linux/sync_file.h
 F:	include/uapi/linux/sync_file.h