Bluetooth: hci_{ldisc,serdev}: check percpu_init_rwsem() failure

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_{ldisc,serdev}: check percpu_init_rwsem() failure syzbot is reporting NULL pointer dereference at hci_uart_tty_close() [1], for rcu_sync_enter() is called without rcu_sync_init() due to hci_uart_tty_open() ignoring percpu_init_rwsem() failure. While we are at it, fix that hci_uart_register_device() ignores percpu_init_rwsem() failure and hci_uart_unregister_device() does not call percpu_free_rwsem().