drm/ttm: remove ttm_buffer_object->buffer_start

All drivers set it to 0 and nothing uses it.

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/mgag200/mgag200_ttm.c b/drivers/gpu/drm/mgag200/mgag200_ttm.c
index 1504699..49d60a6 100644
--- a/drivers/gpu/drm/mgag200/mgag200_ttm.c
+++ b/drivers/gpu/drm/mgag200/mgag200_ttm.c
@@ -355,7 +355,7 @@
 
 	ret = ttm_bo_init(&mdev->ttm.bdev, &mgabo->bo, size,
 			  ttm_bo_type_device, &mgabo->placement,
-			  align >> PAGE_SHIFT, 0, false, NULL, acc_size,
+			  align >> PAGE_SHIFT, false, NULL, acc_size,
 			  NULL, mgag200_bo_ttm_destroy);
 	if (ret)
 		return ret;