mdio-sun4i: oops in error handling in probe

BugLink: https://bugs.launchpad.net/bugs/1878232

commit 227f33be upstream.

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

Fixes: 4bdcb1dd ('net: Add MDIO bus driver for the Allwinner EMAC')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/net/phy/mdio-sun4i.c

@@ -134,6 +134,7 @@ static int sun4i_mdio_probe(struct platform_device *pdev)
 		}
 
 		dev_info(&pdev->dev, "no regulator found\n");
+		data->regulator = NULL;
 	} else {
 		ret = regulator_enable(data->regulator);
 		if (ret)
@@ -149,7 +150,8 @@ static int sun4i_mdio_probe(struct platform_device *pdev)
 	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;