zink: add an assert to verify that deferred clears aren't added in renderpass

this would be very, very broken

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17640>

src/gallium/drivers/zink/zink_clear.c

@@ -291,6 +291,7 @@ zink_clear(struct pipe_context *pctx,
       else
          ctx->rp_clears_enabled |= (buffers & PIPE_CLEAR_DEPTHSTENCIL);
    }
+   assert(!ctx->batch.in_rp);
    ctx->rp_changed |= ctx->rp_clears_enabled != rp_clears_enabled;
 }