r600: don't try to serialized shaders translated from TGSI

TTN seems to have a problem encoding vec4[4] correctly, so that
serialization might fail.

Related: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7891

Fixes: 5b205ef (r600: Store nir shaders serialized to save memory)

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20355>

src/gallium/drivers/r600/r600_shader.c

@@ -395,7 +395,7 @@ int r600_pipe_shader_create(struct pipe_context *ctx,
 			   shader->shader.bc.ncf,
 			   shader->shader.bc.nstack);
 
-	if (!sel->nir_blob && sel->nir) {
+	if (!sel->nir_blob && sel->nir && sel->ir_type != PIPE_SHADER_IR_TGSI) {
 		struct blob blob;
 		blob_init(&blob);
 		nir_serialize(&blob, sel->nir, false);