net-next: ax88796: release platform device drvdata on probe error and module remove

The net device struct pointer is stored as platform device drvdata on
module probe - clear the drvdata entry on probe fail there, as well as
when unloading the module.

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>