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>
diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
index 6ee2e4f..648c609 100644
--- a/scripts/kconfig/expr.h
+++ b/scripts/kconfig/expr.h
@@ -18,7 +18,7 @@
 struct file {
 	struct file *next;
 	struct file *parent;
-	char *name;
+	const char *name;
 	int lineno;
 	int flags;
 };