net: netsec: fix error handling in netsec_register_mdio()

In the Linux kernel, the following vulnerability has been resolved:

net: netsec: fix error handling in netsec_register_mdio()

If phy_device_register() fails, phy_device_free() need be called to

put refcount, so memory of phy device and device name can be freed

in callback function.

If get_phy_device() fails, mdiobus_unregister() need be called,

or it will cause warning in mdiobus_free() and kobject is leaked.