net: mvmdio: avoid error message for optional IRQ

Per the dt-binding the interrupt is optional so use
platform_get_irq_optional() instead of platform_get_irq(). Since
commit 7723f4c5ecdb ("driver core: platform: Add an error message to
platform_get_irq*()") platform_get_irq() produces an error message

  orion-mdio f1072004.mdio: IRQ index 0 not found

which is perfectly normal if one hasn't specified the optional property
in the device tree.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/marvell/mvmdio.c b/drivers/net/ethernet/marvell/mvmdio.c
index 0b9e851..d2e2dc5 100644
--- a/drivers/net/ethernet/marvell/mvmdio.c
+++ b/drivers/net/ethernet/marvell/mvmdio.c
@@ -347,7 +347,7 @@
 	}
 
 
-	dev->err_interrupt = platform_get_irq(pdev, 0);
+	dev->err_interrupt = platform_get_irq_optional(pdev, 0);
 	if (dev->err_interrupt > 0 &&
 	    resource_size(r) < MVMDIO_ERR_INT_MASK + 4) {
 		dev_err(&pdev->dev,
@@ -364,8 +364,8 @@
 		writel(MVMDIO_ERR_INT_SMI_DONE,
 			dev->regs + MVMDIO_ERR_INT_MASK);
 
-	} else if (dev->err_interrupt == -EPROBE_DEFER) {
-		ret = -EPROBE_DEFER;
+	} else if (dev->err_interrupt < 0) {
+		ret = dev->err_interrupt;
 		goto out_mdio;
 	}