tty: serial: ma35d1: Add a NULL check for of_node

The pdev->dev.of_node can be NULL if the "serial" node is absent.
Add a NULL check to return an error in such cases.

Fixes: 930cbf9 ("tty: serial: Add Nuvoton ma35d1 serial driver support")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/8df7ce45-fd58-4235-88f7-43fe7cd67e8f@moroto.mountain/
Signed-off-by: Jacky Huang <ychuang3@nuvoton.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/20240625064128.127-1-ychuang570808@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ychuang3

drivers/tty/serial/ma35d1_serial.c

@@ -688,12 +688,13 @@ static int ma35d1serial_probe(struct platform_device *pdev)
 	struct uart_ma35d1_port *up;
 	int ret = 0;
 
-	if (pdev->dev.of_node) {
-		ret = of_alias_get_id(pdev->dev.of_node, "serial");
-		if (ret < 0) {
-			dev_err(&pdev->dev, "failed to get alias/pdev id, errno %d\n", ret);
-			return ret;
-		}
+	if (!pdev->dev.of_node)
+		return -ENODEV;
+
+	ret = of_alias_get_id(pdev->dev.of_node, "serial");
+	if (ret < 0) {
+		dev_err(&pdev->dev, "failed to get alias/pdev id, errno %d\n", ret);
+		return ret;
 	}
 	up = &ma35d1serial_ports[ret];
 	up->port.line = ret;