topo_expl: fix build after switching to rocm-smi-lib (#405)

* topo_expl: fix build after switching to rocm-smi-lib

* Use minimal of 4 channels for gfx908

src/init.cc

@@ -865,6 +865,8 @@ static ncclResult_t initTransportsRank(struct ncclComm* comm, ncclUniqueId* comm
   int idx;
   NCCLCHECK(ncclTopoIdToIndex(comm->topo, GPU, myInfo->busId, &idx));
   allGather3Data[rank].nc = 2;
+  if (comm->topo->nodes[GPU].nodes[idx].gpu.gcn == 908)
+    allGather3Data[rank].nc = std::max(4/ringGraph.nChannels, 2);
   if (comm->topo->nodes[GPU].count == comm->topo->nRanks && (comm->topo->type & RCCL_TOPO_CR8G))
     allGather3Data[rank].nc = 4;
   if (comm->topo->nodes[GPU].count == comm->topo->nRanks && comm->topo->nodes[GPU].nodes[idx].gpu.gcn == 910)