serial: 8250_mtk: Switch to use platform_get_irq()

platform_get_irq() provides an established error code and error message.
Also, it's better to use dedicated API to retrieve Linux IRQ resource.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20200618122952.88265-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_mtk.c

@@ -494,13 +494,17 @@ static int mtk8250_probe_of(struct platform_device *pdev, struct uart_port *p,
 static int mtk8250_probe(struct platform_device *pdev)
 {
 	struct uart_8250_port uart = {};
-	struct resource *regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	struct resource *irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
 	struct mtk8250_data *data;
-	int err;
+	struct resource *regs;
+	int irq, err;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
 
-	if (!regs || !irq) {
-		dev_err(&pdev->dev, "no registers/irq defined\n");
+	regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!regs) {
+		dev_err(&pdev->dev, "no registers defined\n");
 		return -EINVAL;
 	}
 
@@ -524,7 +528,7 @@ static int mtk8250_probe(struct platform_device *pdev)
 
 	spin_lock_init(&uart.port.lock);
 	uart.port.mapbase = regs->start;
-	uart.port.irq = irq->start;
+	uart.port.irq = irq;
 	uart.port.pm = mtk8250_do_pm;
 	uart.port.type = PORT_16550;
 	uart.port.flags = UPF_BOOT_AUTOCONF | UPF_FIXED_PORT;