clk: add static qualifier to local functions

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/clk/clk_rk3288.c b/drivers/clk/clk_rk3288.c
index 54d4930..0172ad1 100644
--- a/drivers/clk/clk_rk3288.c
+++ b/drivers/clk/clk_rk3288.c
@@ -508,7 +508,7 @@
 	return rockchip_spi_get_clk(cru, clk_general_rate, periph);
 }
 
-ulong rk3288_set_periph_rate(struct udevice *dev, int periph, ulong rate)
+static ulong rk3288_set_periph_rate(struct udevice *dev, int periph, ulong rate)
 {
 	struct rk3288_clk_priv *priv = dev_get_priv(dev);
 	ulong new_rate;