kconfig: begin PARAM state only when seeing a command keyword

Currently, any statement line starts with a keyword with TF_COMMAND
flag.  So, the following three lines are dead code.

        alloc_string(yytext, yyleng);
        zconflval.string = text;
        return T_WORD;

If a T_WORD token is returned in this context, it will cause syntax
error in the parser anyway.

The next commit will support the assignment statement where a line
starts with an arbitrary identifier.  So, I want the lexer to switch
to the PARAM state only when it sees a command keyword.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/zconf.l

@@ -102,10 +102,10 @@ n	[A-Za-z0-9_-]
 <COMMAND>{
 	{n}+	{
 		const struct kconf_id *id = kconf_id_lookup(yytext, yyleng);
-		BEGIN(PARAM);
 		current_pos.file = current_file;
 		current_pos.lineno = yylineno;
 		if (id && id->flags & TF_COMMAND) {
+			BEGIN(PARAM);
 			yylval.id = id;
 			return id->token;
 		}