dma-buf/sync_file: hold reference to fence when creating sync_file

fence referencing was out of balance. It was not taking any ref to the
fence at creating time, but it was putting a reference when freeing the
sync file.

This patch fixes the balancing issue by getting a reference for the fence
when creating the sync_file.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1476899313-22241-1-git-send-email-gustavo@padovan.org

drivers/dma-buf/sync_file.c

@@ -79,7 +79,7 @@ struct sync_file *sync_file_create(struct fence *fence)
 	if (!sync_file)
 		return NULL;
 
-	sync_file->fence = fence;
+	sync_file->fence = fence_get(fence);
 
 	snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
 		 fence->ops->get_driver_name(fence),