For now, I suppose that s simple fix could be to use an anonymous clock
request when probed via DT. This code you quote dates from 2008 when
there was no clkdev in the kernel at all. So something like this would
probably do it for now:

diff --git a/drivers/tty/serial/bcm63xx_uart.c

b/drivers/tty/serial/bcm63xx_uart.c
index e0b87d507670..1b914b85dd31 100644

--- a/drivers/tty/serial/bcm63xx_uart.c
+++ b/drivers/tty/serial/bcm63xx_uart.c

@@ -819,7 +819,7 @@ static int bcm_uart_probe(struct platform_device *pdev)
        if (!res_irq)
                return -ENODEV;

-       clk = clk_get(&pdev->dev, "periph");
+       clk = clk_get(&pdev->dev, pdev->dev.of_node ? NULL : "periph");
        if (IS_ERR(clk))
                return -ENODEV;