pb_type: fix addition of blif model to muxes

Signed-off-by: Alessandro Comodi <acomodi@antmicro.com>

v2x/vlog_to_pbtype.py

diff --git a/v2x/vlog_to_pbtype.py b/v2x/vlog_to_pbtype.py
index 338a766..54bdc8c 100755
--- a/v2x/vlog_to_pbtype.py
+++ b/v2x/vlog_to_pbtype.py
@@ -787,7 +787,7 @@
             # TODO: pb_attrs["class"] = "routing"
             pass
         elif mod_cls == "mux":
-            # TODO: ?
+            pb_attrs["blif_model"] = ".subckt " + model_name
             pass
         elif mod_cls == "flipflop":
             pb_attrs["blif_model"] = ".latch"