Bluetooth: Fix clearing SMP keys if pairing fails

If SMP fails we should not leave any keys (LTKs or IRKs) hanging around
the internal lists. This patch adds the necessary code to
smp_chan_destroy to remove any keys we may have in case of pairing
failure.

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