serial: sh-sci: Use platform_get_irq_optional() for optional interrupts

As platform_get_irq() now prints an error when the interrupt does not
exist, scary warnings may be printed for optional interrupts:

    sh-sci e6550000.serial: IRQ index 1 not found
    sh-sci e6550000.serial: IRQ index 2 not found
    sh-sci e6550000.serial: IRQ index 3 not found
    sh-sci e6550000.serial: IRQ index 4 not found
    sh-sci e6550000.serial: IRQ index 5 not found

Fix this by calling platform_get_irq_optional() instead for all but the
first interrupts, which are optional.

Fixes: 7723f4c5 ("driver core: platform: Add an error message to platform_get_irq*()")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20191001180743.1041-1-geert+renesas@glider.beSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -2894,8 +2894,12 @@ static int sci_init_single(struct platform_device *dev,
 	port->mapbase = res->start;
 	sci_port->reg_size = resource_size(res);
 
-	for (i = 0; i < ARRAY_SIZE(sci_port->irqs); ++i)
+	for (i = 0; i < ARRAY_SIZE(sci_port->irqs); ++i) {
+		if (i)
+			sci_port->irqs[i] = platform_get_irq_optional(dev, i);
+		else
 			sci_port->irqs[i] = platform_get_irq(dev, i);
+	}
 
 	/* The SCI generates several interrupts. They can be muxed together or
 	 * connected to different interrupt lines. In the muxed case only one