mdio-sun4i: oops in error handling in probe

We could end up dereferencing an error pointer when we call
regulator_disable().

Fixes: 4bdcb1dd9feb ('net: Add MDIO bus driver for the Allwinner EMAC')
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Chen-Yu Tsai <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/phy/mdio-sun4i.c

···
 			return -EPROBE_DEFER;
 
 		dev_info(&pdev->dev, "no regulator found\n");
+		data->regulator = NULL;
 	} else {
 		ret = regulator_enable(data->regulator);
 		if (ret)
···
 	return 0;
 
 err_out_disable_regulator:
-	regulator_disable(data->regulator);
+	if (data->regulator)
+		regulator_disable(data->regulator);
 err_out_free_mdiobus:
 	mdiobus_free(bus);
 	return ret;