Bluetooth: hci_bcm: Fix crash on suspend

If bcm_suspend is called whithout device opened there is a crash as
it tries to use bdev->hu which is NULL.
Rename bcm_device_list_lock to bcm_device_lock as it does not only apply
to bcm_device_list.

Signed-off-by: Frederic Danis <frederic.danis@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>