Flat router sync assigns same pb_graph_pin to all equivalent pins

[amin1377]

In the function that updates stored intra-cluster routing with routing results (when the flat router is used), the sync logic fails if two pins of a block (e.g., a LUT) are connected to the same net. Specifically, this code
iterates over all pins of a port (where pins are equivalent) and assigns the same t_pb_graph_pin to all pins connected to that net, which is incorrect.

[amin1377]

@duck2: When you have time, please let me know what you think. Thanks!

[duck2]

That lookup took a lot of reverse engineering to piece together so there may be errors. No idea why that fails though