drm/vmwgfx: Fix Use-after-free in validation

In the Linux kernel, the following vulnerability has been resolved: drm/vmwgfx: Fix Use-after-free in validation Nodes stored in the validation duplicates hashtable come from an arena allocator that is cleared at the end of vmw_execbuf_process. All nodes are expected to be cleared in vmw_validation_drop_ht but this node escaped because its resource was destroyed prematurely.