Bluetooth: h5: Fix missing dependency on BT_HCIUART_SERDEV

This driver was recently updated to use serdev, so add the appropriate
dependency. Without this one can get compiler warnings like this if
CONFIG_SERIAL_DEV_BUS is not enabled:

  CC [M]  drivers/bluetooth/hci_h5.o
drivers/bluetooth/hci_h5.c:934:36: warning: ‘h5_serdev_driver’ defined but not used [-Wunused-variable]
 static struct serdev_device_driver h5_serdev_driver = {
                                    ^~~~~~~~~~~~~~~~

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>