ice40: Map unmapped 'mince' DFFs to gate level

Signed-off-by: David Shah <dave@ds0.me>

techlibs/ice40/synth_ice40.cc

@@ -345,6 +345,7 @@ struct SynthIce40Pass : public ScriptPass
 			if (min_ce_use >= 0) {
 				run("opt_merge");
 				run(stringf("dff2dffe -unmap-mince %d", min_ce_use));
+				run("simplemap t:$dff");
 			}
 			run("techmap -D NO_LUT -D NO_ADDER -map +/ice40/cells_map.v");
 			run("opt_expr -mux_undef");