disable generation of unput() and input() in lexer to avoid code check fail

src/lex/lexer.l

@@ -6,6 +6,11 @@
     int yylex();
 %}
 
+// disable the following functions
+// to avoid failing code check
+%option nounput
+%option noinput
+
 %%
 .;
-%%
+%%