Move DSM segment comment to correct place

Author: syvb

pgvectorscale/src/access_method/build.rs

@@ -367,6 +367,7 @@ pub extern "C-unwind" fn ambuild(
             parallel::toc_estimate_single_chunk(pcxt, tablescandesc_size_estimate);
 
             pg_sys::InitializeParallelDSM(pcxt);
+            // need DSM segment to do parallel build
             if (*pcxt).seg.is_null() {
                 parallel::cleanup_parallel_context(pcxt, snapshot);
                 None

pgvectorscale/src/access_method/build/parallel.rs

@@ -20,7 +20,6 @@ pub unsafe fn cleanup_parallel_context(
     pcxt: *mut pg_sys::ParallelContext,
     snapshot: *mut pg_sys::SnapshotData,
 ) {
-    // need DSM segment to do parallel build
     if ports::is_mvcc_snapshot(snapshot) {
         pg_sys::UnregisterSnapshot(snapshot);
     }