fsl_lpuart: Don't enable interrupts too early

If an irq is pending when devm_request_irq() is called, the irq
handler will cause a NULL pointer access because initialisation
is not done yet.

Fixes: 9d7ee0e28da59 ("tty: serial: lpuart: avoid report NULL interrupt")
Cc: stable <[e-mail]>
Signed-off-by: Indan Zupancic <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/fsl_lpuart.c

···
 	struct device_node *np = pdev->dev.of_node;
 	struct lpuart_port *sport;
 	struct resource *res;
+	irq_handler_t handler;
 	int ret;
 
 	sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
···
 
 	if (lpuart_is_32(sport)) {
 		lpuart_reg.cons = LPUART32_CONSOLE;
-		ret = devm_request_irq(&pdev->dev, sport->port.irq, lpuart32_int, 0,
-					DRIVER_NAME, sport);
+		handler = lpuart32_int;
 	} else {
 		lpuart_reg.cons = LPUART_CONSOLE;
-		ret = devm_request_irq(&pdev->dev, sport->port.irq, lpuart_int, 0,
-					DRIVER_NAME, sport);
+		handler = lpuart_int;
 	}
-
-	if (ret)
-		goto failed_irq_request;
-
 	ret = uart_add_one_port(&lpuart_reg, &sport->port);
 	if (ret)
 		goto failed_attach_port;
···
 
 	sport->port.rs485_config(&sport->port, &sport->port.rs485);
 
+	ret = devm_request_irq(&pdev->dev, sport->port.irq, handler, 0,
+				DRIVER_NAME, sport);
+	if (ret)
+		goto failed_irq_request;
+
 	return 0;
 
+failed_irq_request:
 failed_get_rs485:
 failed_reset:
 	uart_remove_one_port(&lpuart_reg, &sport->port);
 failed_attach_port:
-failed_irq_request:
 	lpuart_disable_clks(sport);
 failed_clock_enable:
 failed_out_of_range: