freedreno/ir3: we require block_index metadata

Found during NIR_TEST_CLONE=1 piglit run.  We were using block->index
but forgetting to require it.  Causing things to not work with a cloned
shader which didn't preserve block_index.

Signed-off-by: Rob Clark <robclark@freedesktop.org>

src/gallium/drivers/freedreno/ir3/ir3_compiler_nir.c

@@ -2098,6 +2098,8 @@ emit_stream_out(struct ir3_compile *ctx)
 static void
 emit_function(struct ir3_compile *ctx, nir_function_impl *impl)
 {
+	nir_metadata_require(impl, nir_metadata_block_index);
+
 	emit_cf_list(ctx, &impl->body);
 	emit_block(ctx, impl->end_block);