rockchip: Use rockchip_get_clk() to obtain the SoC clock

The current code picks the first available clock. In U-Boot proper this is
the oscillator device, not the SoC clock device. As a result the HDMI display
does not work.

Fix this by calling rockchip_get_clk() instead.

Fixes: 135aa950 (clk: convert API to match reset/mailbox style)
Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
diff --git a/drivers/clk/clk_rk3288.c b/drivers/clk/clk_rk3288.c
index a41cf8b..e00feb0 100644
--- a/drivers/clk/clk_rk3288.c
+++ b/drivers/clk/clk_rk3288.c
@@ -145,7 +145,7 @@
 	struct udevice *dev;
 	int ret;
 
-	ret = uclass_get_device(UCLASS_CLK, 0, &dev);
+	ret = rockchip_get_clk(&dev);
 	if (ret)
 		return ERR_PTR(ret);