tty: serial: imx: Use platform_get_irq_optional() for optional IRQs

All i.MX SoCs except i.MX1 have ONLY one necessary IRQ, use
platform_get_irq_optional() to get second/third IRQ which are
optional to avoid below error message during probe:

[    0.726219] imx-uart 30860000.serial: IRQ index 1 not found
[    0.731329] imx-uart 30860000.serial: IRQ index 2 not found

Fixes: 7723f4c5 ("driver core: platform: Add an error message to platform_get_irq*()")
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Link: https://lore.kernel.org/r/1570614559-11900-1-git-send-email-Anson.Huang@nxp.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -2222,8 +2222,8 @@ static int imx_uart_probe(struct platform_device *pdev)
 		return PTR_ERR(base);
 
 	rxirq = platform_get_irq(pdev, 0);
-	txirq = platform_get_irq(pdev, 1);
-	rtsirq = platform_get_irq(pdev, 2);
+	txirq = platform_get_irq_optional(pdev, 1);
+	rtsirq = platform_get_irq_optional(pdev, 2);
 
 	sport->port.dev = &pdev->dev;
 	sport->port.mapbase = res->start;