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/arch/arm/mach-rockchip/board.c b/arch/arm/mach-rockchip/board.c
index f662b26..bec756d 100644
--- a/arch/arm/mach-rockchip/board.c
+++ b/arch/arm/mach-rockchip/board.c
@@ -178,7 +178,7 @@
 	int ret, i;
 	struct udevice *dev;
 
-	ret = uclass_get_device(UCLASS_CLK, 0, &dev);
+	ret = rockchip_get_clk(&dev);
 	if (ret) {
 		printf("clk-uclass not found\n");
 		return 0;