use correct pointer in the math

Author: tony2001

ext/standard/array.c

@@ -268,7 +268,7 @@ static int php_array_key_compare_string(const void *a, const void *b) /* {{{ */
 l2 = s->key->len;
 } else {
 s2 = zend_print_long_to_buf(buf2 + sizeof(buf2) - 1, s->h);
-l2 = buf2 + sizeof(buf2) - 1 - s1;
+l2 = buf2 + sizeof(buf2) - 1 - s2;
 }
 return zend_binary_strcmp(s1, l1, s2, l2);
 }