Fix wrong function name in comment.

Rushabh Lathia

Discussion: http://postgr.es/m/CAGPqQf2z5g+7YmGZSZgKoiFsaUB+63Rzmz8-5PQHuS6hd14FEg@mail.gmail.com

src/backend/executor/execPartition.c

@@ -472,7 +472,7 @@ FormPartitionKeyDatum(PartitionDispatch pd,
 }
 
 /*
- * BuildSlotPartitionKeyDescription
+ * ExecBuildSlotPartitionKeyDescription
  *
  * This works very much like BuildIndexValueDescription() and is currently
  * used for building error messages when ExecFindPartition() fails to find