Bluetooth: Fix hci core device initialization

We must not call device_del() if we didn't use device_add(). See module.c
for comments on that. Therefore, we need to call device_initialize() when
allocating the hci device and later device_add() instead of
device_register().

This also fixes a bug when hci_register_dev() failed and we call
hci_free_dev() without a valid core device. hci_free_dev() segfaults while
calling put_device() on invalid memory.

We already do this with hci_conn connections (hci_conn_init_sysfs()) so
they do not need to be fixed.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>