kconfig: constify file name

Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/expr.h

@@ -18,7 +18,7 @@ extern "C" {
 struct file {
 	struct file *next;
 	struct file *parent;
-	char *name;
+	const char *name;
 	int lineno;
 	int flags;
 };