zink: do not destroy staging-resource, deref it

Acked-by: Jordan Justen <jordan.l.justen@intel.com>
diff --git a/src/gallium/drivers/zink/zink_resource.c b/src/gallium/drivers/zink/zink_resource.c
index 24dc051..34c7ed0 100644
--- a/src/gallium/drivers/zink/zink_resource.c
+++ b/src/gallium/drivers/zink/zink_resource.c
@@ -493,8 +493,7 @@
          zink_transfer_copy_bufimage(ctx, res, staging_res, trans, true);
       }
 
-      zink_resource_destroy(pctx->screen, trans->staging_res);
-      trans->staging_res = NULL;
+      pipe_resource_reference(&trans->staging_res, NULL);
    } else
       vkUnmapMemory(screen->dev, res->mem);