phy: renesas: rcar-gen3-usb2: Use platform_get_irq_optional() for optional irq

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

    phy_rcar_gen3_usb2 ee0a0200.usb-phy: IRQ index 0 not found

Fix this by calling platform_get_irq_optional() instead.

Fixes: 7723f4c5 ("driver core: platform: Add an error message to platform_get_irq*()")
Reviewed-by: NStephen Boyd <swboyd@chromium.org>
Reviewed-by: NYoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: NYoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

drivers/phy/renesas/phy-rcar-gen3-usb2.c

@@ -614,7 +614,7 @@ static int rcar_gen3_phy_usb2_probe(struct platform_device *pdev)
 		return PTR_ERR(channel->base);
 
 	/* call request_irq for OTG */
-	irq = platform_get_irq(pdev, 0);
+	irq = platform_get_irq_optional(pdev, 0);
 	if (irq >= 0) {
 		INIT_WORK(&channel->work, rcar_gen3_phy_usb2_work);
 		irq = devm_request_irq(dev, irq, rcar_gen3_phy_usb2_irq,