hsr: hold rcu and dev lock for hsr_get_port_ndev

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

hsr: hold rcu and dev lock for hsr_get_port_ndev

hsr_get_port_ndev calls hsr_for_each_port, which need to hold rcu lock. On the other hand, before return the port device, we need to hold the device reference to avoid UaF in the caller function.