kconfig: make conf_get_autoconfig_name() static

This is only used in confdata.c

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
index 8bb74d4..492ac34 100644
--- a/scripts/kconfig/confdata.c
+++ b/scripts/kconfig/confdata.c
@@ -226,7 +226,7 @@ const char *conf_get_configname(void)
 	return name ? name : ".config";
 }
 
-const char *conf_get_autoconfig_name(void)
+static const char *conf_get_autoconfig_name(void)
 {
 	char *name = getenv("KCONFIG_AUTOCONFIG");