nbc ireduce_scatter: ensure to check the correct return code

This was CID 1196644 and 1196621

ompi/mca/coll/libnbc/nbc_ireduce_scatter.c

@@ -180,7 +180,7 @@ int ompi_coll_libnbc_ireduce_scatter_inter(void* sendbuf, void* recvbuf, int *re
   if (MPI_SUCCESS != res) { printf("MPI Error in MPI_Comm_rank() (%i)\n", res); return res; }
   res = MPI_Comm_remote_size(comm, &rsize);
   if (MPI_SUCCESS != res) { printf("MPI Error in MPI_Comm_remote_size() (%i)\n", res); return res; }
-  MPI_Type_extent(datatype, &ext);
+  res = MPI_Type_extent(datatype, &ext);
   if (MPI_SUCCESS != res) { printf("MPI Error in MPI_Type_extent() (%i)\n", res); return res; }
 
   schedule = (NBC_Schedule*)malloc(sizeof(NBC_Schedule));