i965/nir: Temporariliy disable mul+add fusion

We don't want to do this in the long-run but it's needed for passing the
NoContraction tests at the moment.  Eventually, we want to plumb this
through NIR properly.

src/mesa/drivers/dri/i965/brw_nir.c

@@ -535,7 +535,7 @@ brw_postprocess_nir(nir_shader *nir,
 
    if (devinfo->gen >= 6) {
       /* Try and fuse multiply-adds */
-      OPT(brw_nir_opt_peephole_ffma);
+//      OPT(brw_nir_opt_peephole_ffma);
    }
 
    OPT(nir_opt_algebraic_late);