Bluetooth: Fix missing return statement in process_adv_report

If we're doing passive scanning we shouldn't proceed with any of the
code that deals with active scanning (pending reports, etc.). This patch
fixes a missing return statement for the passive scanning section in the
process_adv_report() function.

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