serial: stm32: Convert to platform remove callback returning void

The .remove() callback for a platform driver returns an int which makes
many driver authors wrongly assume it's possible to do error handling by
returning an error code. However the value returned is ignored (apart
from emitting a warning) and this typically results in resource leaks.

To improve here there is a quest to make the remove callback return
void. In the first step of this quest all drivers are converted to
.remove_new(), which already returns void. Eventually after all drivers
are converted, .remove_new() will be renamed to .remove().

Trivially convert this driver from always returning zero in the remove
callback to the void returning variant.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20231110152927.70601-43-u.kleine-koenig@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -1822,7 +1822,7 @@ static int stm32_usart_serial_probe(struct platform_device *pdev)
 	return ret;
 }
 
-static int stm32_usart_serial_remove(struct platform_device *pdev)
+static void stm32_usart_serial_remove(struct platform_device *pdev)
 {
 	struct uart_port *port = platform_get_drvdata(pdev);
 	struct stm32_port *stm32_port = to_stm32_port(port);
@@ -1861,8 +1861,6 @@ static int stm32_usart_serial_remove(struct platform_device *pdev)
 	}
 
 	stm32_usart_deinit_port(stm32_port);
-
-	return 0;
 }
 
 static void __maybe_unused stm32_usart_console_putchar(struct uart_port *port, unsigned char ch)
@@ -2146,7 +2144,7 @@ static const struct dev_pm_ops stm32_serial_pm_ops = {
 
 static struct platform_driver stm32_serial_driver = {
 	.probe		= stm32_usart_serial_probe,
-	.remove		= stm32_usart_serial_remove,
+	.remove_new	= stm32_usart_serial_remove,
 	.driver	= {
 		.name	= DRIVER_NAME,
 		.pm	= &stm32_serial_pm_ops,