Make hci_uart_register_device() and hci_uart_unregister_device() call
serdev_device_close()/open() themselves instead of relying on the various
hci_uart drivers to do this for them.

Besides reducing code complexity, this also ensures correct error checking
of serdev_device_open(), which was missing in a few drivers.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>