Remove one use of pg_atoi()

There was no real need to use this here instead of a simpler API.

Reviewed-by: John Naylor <john.naylor@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/b239564c-cad0-b23e-c57e-166d883cb97d@enterprisedb.com

src/backend/utils/adt/jsonpath_gram.y

@@ -232,7 +232,7 @@ array_accessor:
 	;
 
 any_level:
-	INT_P							{ $$ = pg_atoi($1.val, 4, 0); }
+	INT_P							{ $$ = pg_strtoint32($1.val); }
 	| LAST_P						{ $$ = -1; }
 	;