fix sampling handling of dscr region (#2321)

Bug was discovered in how the sampling code is looking up DCSR offset.

Authors:
  - Chuck Hastings (https://github.com/ChuckHastings)

Approvers:
  - Brad Rees (https://github.com/BradReesWork)
  - Seunghwa Kang (https://github.com/seunghwak)

URL: #2321

cpp/src/sampling/detail/sampling_utils_impl.cuh

@@ -504,7 +504,7 @@ gather_local_edges(
           auto row_hypersparse_idx =
             partitions[partition_id].major_hypersparse_idx_from_major_nocheck(major);
           if (row_hypersparse_idx) {
-            location_in_segment = *(row_hypersparse_idx)-id_begin[partition_id];
+            location_in_segment = *row_hypersparse_idx;
           } else {
             minors[index] = invalid_vertex_id;
             return;