Bluetooth: Fix memory leak in le_scan_disable_work_complete()

The hci_request in le_scan_disable_work_complete() was being initialized
in a general context but only used in a specific branch in the function
(when simultaneous discovery is not supported). This patch moves the
usage to be limited to the branch where hci_req_run() is actually
called.

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