serial: zynq: Fix address reading from DM

Use dev_get_addr() instead of reading reg base directly in the driver.
Core function is also more robust.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/drivers/serial/serial_zynq.c b/drivers/serial/serial_zynq.c
index 112a7a2..e79d997 100644
--- a/drivers/serial/serial_zynq.c
+++ b/drivers/serial/serial_zynq.c
@@ -156,13 +156,8 @@
 static int zynq_serial_ofdata_to_platdata(struct udevice *dev)
 {
 	struct zynq_uart_priv *priv = dev_get_priv(dev);
-	fdt_addr_t addr;
 
-	addr = fdtdec_get_addr(gd->fdt_blob, dev->of_offset, "reg");
-	if (addr == FDT_ADDR_T_NONE)
-		return -EINVAL;
-
-	priv->regs = (struct uart_zynq *)addr;
+	priv->regs = (struct uart_zynq *)dev_get_addr(dev);
 
 	return 0;
 }