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/zconf.l b/scripts/kconfig/zconf.l
index d8f7236..2b02650 100644
--- a/scripts/kconfig/zconf.l
+++ b/scripts/kconfig/zconf.l
@@ -353,7 +353,7 @@
 	return current_pos.lineno;
 }
 
-char *zconf_curname(void)
+const char *zconf_curname(void)
 {
 	return current_pos.file ? current_pos.file->name : "<none>";
 }