Bluetooth: Remove redundant NULL check

All callers of hci_inquiry_cache_update() pass a non-NULL ssp pointer to
it and even the function itself assumes in another place that the
pointer is non-NULL. Therefore, remove the redundant check.

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