drm/i810: off by one in i810_dma_vertex()

If vertex->idx == dma->buf_count then we end up reading one element
beyond the end of the dma->buflist[] array.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703123015.kma7v7rwtdy4urce@kili.mountain

drivers/gpu/drm/i810/i810_dma.c

@@ -934,7 +934,7 @@ static int i810_dma_vertex(struct drm_device *dev, void *data,
 	DRM_DEBUG("idx %d used %d discard %d\n",
 		  vertex->idx, vertex->used, vertex->discard);
 
-	if (vertex->idx < 0 || vertex->idx > dma->buf_count)
+	if (vertex->idx < 0 || vertex->idx >= dma->buf_count)
 		return -EINVAL;
 
 	i810_dma_dispatch_vertex(dev,