nir: Call nir_metadata_preserve on !progress

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5171>

src/compiler/nir/nir_split_var_copies.c

@@ -121,9 +121,7 @@ split_var_copies_impl(nir_function_impl *impl)
       nir_metadata_preserve(impl, nir_metadata_block_index |
                                   nir_metadata_dominance);
    } else {
-#ifndef NDEBUG
-      impl->valid_metadata &= ~nir_metadata_not_properly_reset;
-#endif
+      nir_metadata_preserve(impl, nir_metadata_all);
    }
 
    return progress;