Bluetooth: Fix calling hci_conn_put too early

The pairing_complete() function relies on a hci_conn reference to be
able to access the hci_conn object. It should therefore only release
this reference once it's done accessing the object, i.e. at the end of
the function.

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