Fix get_relation_info name typo'ed in a comment

Plus add a missing comment about this in get_relation_info itself.

Author: Amit Langote
Discussion: https://postgr.es/m/e46c0569-0449-afa0-e2fe-f3776e4b3fd5@lab.ntt.co.jp

src/backend/optimizer/util/plancat.c

@@ -78,6 +78,7 @@ static List *build_index_tlist(PlannerInfo *root, IndexOptInfo *index,
  *	fdwroutine	if it's a foreign table, the FDW function pointers
  *	pages		number of pages
  *	tuples		number of tuples
+ *	rel_parallel_workers user-defined number of parallel workers
  *
  * Also, add information about the relation's foreign keys to root->fkey_list.
  *

src/backend/optimizer/util/relnode.c

@@ -126,7 +126,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->allvisfrac = 0;
 	rel->subroot = NULL;
 	rel->subplan_params = NIL;
-	rel->rel_parallel_workers = -1;		/* set up in GetRelationInfo */
+	rel->rel_parallel_workers = -1;		/* set up in get_relation_info */
 	rel->serverid = InvalidOid;
 	rel->userid = rte->checkAsUser;
 	rel->useridiscurrent = false;