Comment fixups from 626df47ad9.

Reported-by: Peter Smith <smithpb2250@gmail.com>
Discussion: https://postgr.es/m/CAHut+PspbHQmRCBL1c-opoJeTUKUaFFfUQJd2rhDZqwUrWCi7w@mail.gmail.com

src/backend/executor/execGrouping.c

@@ -144,7 +144,7 @@ execTuplesHashPrepare(int numCols,
  *	hashfunctions: FmgrInfos of datatype-specific hashing functions to use
  *	collations: collations to use in comparisons
  *	nbuckets: initial estimate of hashtable size
- *	additionalsize: size of data stored in ->additional
+ *	additionalsize: size of data that may be stored along with the hash entry
  *	metacxt: memory context for long-lived allocation, but not per-entry data
  *	tablecxt: memory context in which to store table entries
  *	tempcxt: short-lived context for evaluation hash and comparison functions
@@ -288,7 +288,7 @@ ResetTupleHashTable(TupleHashTable hashtable)
  *
  * If isnew isn't NULL, then a new entry is created if no existing entry
  * matches.  On return, *isnew is true if the entry is newly created,
- * false if it existed already.  ->additional_data in the new entry has
+ * false if it existed already.  The additional data in the new entry has
  * been zeroed.
  */
 TupleHashEntry