net: phy: mdio-bcm-unimac: Fix clock handling

The DT binding for this PHY describes an *optional* clock property.
Due to a bug in the error handling logic, we are actually ignoring this
clock *all* of the time so far.

Fix this by using devm_clk_get_optional() to handle this clock properly.

Fixes: b78ac6ec ("net: phy: mdio-bcm-unimac: Allow configuring MDIO clock divider")
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mdio-bcm-unimac.c

@@ -242,11 +242,9 @@ static int unimac_mdio_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	}
 
-	priv->clk = devm_clk_get(&pdev->dev, NULL);
-	if (PTR_ERR(priv->clk) == -EPROBE_DEFER)
+	priv->clk = devm_clk_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(priv->clk))
 		return PTR_ERR(priv->clk);
-	else
-		priv->clk = NULL;
 
 	ret = clk_prepare_enable(priv->clk);
 	if (ret)