nbc ireduce_scatter_block: ensure to check the correct return code

This was CID 1196643 and 1196615

ompi/mca/coll/libnbc/coll_libnbc_ireduce_scatter_block.c

@@ -168,7 +168,7 @@ int ompi_coll_libnbc_ireduce_scatter_block_inter(void *sbuf, void *rbuf, int rco
   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(dtype, &ext);
+  res = MPI_Type_extent(dtype, &ext);
   if (MPI_SUCCESS != res) { printf("MPI Error in MPI_Type_extent() (%i)\n", res); return res; }
 
   schedule = (NBC_Schedule*)malloc(sizeof(NBC_Schedule));