etnaviv: reinstate accidentially commented assert

I added this hack to my tree when testing another MR and ended up
squashing it into c2a3236d1a (etnaviv: clean up tiling setup in
etna_compile_rs_state) by accident when doing some changes to this
commit. Reinstate the assert.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16212>

src/gallium/drivers/etnaviv/etnaviv_nir.c

@@ -111,7 +111,7 @@ etna_lower_io(nir_shader *shader, struct etna_shader_variant *v)
                case nir_tex_src_comparator:
                   break;
                default:
-                  //assert(0);
+                  assert(0);
                   break;
                }
             }