dpaa2-eth: put MAC endpoint device on disconnect

In the Linux kernel, the following vulnerability has been resolved: dpaa2-eth: put MAC endpoint device on disconnect fsl_mc_get_endpoint() returns the MAC endpoint device with a reference taken through device_find_child(). The Ethernet connect path stores that device in mac->mc_dev and keeps it for the lifetime of the connected MAC object. However, the disconnect path only disconnects and closes the MAC before freeing the dpaa2_mac object. It does not drop the endpoint device reference stored in mac->mc_dev, so every successful connect leaks that device reference when the MAC is later disconnected. Drop the endpoint device reference after closing the MAC and before freeing the dpaa2_mac object.