serial: stm32: improve platform_get_irq condition handling in init_port

Replace "ret" variable by "irq" variable from platform_get_irq condition
handling in stm32_init_port as suggested by Jiri in "STM32 uart cleanup and
improvement" series review.
This change will prevent port->irq to be unexpectly modified by a potential
change of "ret" value introduced by a new patch.

Suggested-by: Jiri Slaby <[e-mail]>
Signed-off-by: Erwan Le Ray <[e-mail]>

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/stm32-usart.c

···
 {
 	struct uart_port *port = &stm32port->port;
 	struct resource *res;
-	int ret;
+	int ret, irq;
 
-	ret = platform_get_irq(pdev, 0);
-	if (ret <= 0)
-		return ret ? : -ENODEV;
+	irq = platform_get_irq(pdev, 0);
+	if (irq <= 0)
+		return irq ? : -ENODEV;
 
 	port->iotype	= UPIO_MEM;
 	port->flags	= UPF_BOOT_AUTOCONF;
···
 	port->dev	= &pdev->dev;
 	port->fifosize	= stm32port->info->cfg.fifosize;
 	port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_STM32_CONSOLE);
-	port->irq = ret;
+	port->irq = irq;
 	port->rs485_config = stm32_usart_config_rs485;
 
 	ret = stm32_usart_init_rs485(port, pdev);