net: mhi: Fix memory leak in mhi_net_dellink()

In the Linux kernel, the following vulnerability has been resolved: net: mhi: Fix memory leak in mhi_net_dellink() MHI driver registers network device without setting the needs_free_netdev flag, and does NOT call free_netdev() when unregisters network device, which causes a memory leak. This patch calls free_netdev() to fix it since netdev_priv is used after unregister.