Bluetooth: Make hci_pend_le_conn_lookup more general purposed

In some circumstances we need to look up entries in pend_le_conns and in
other in pend_le_reports. This patch converts the existing lookup
function for pend_le_conns to something that can be used for both lists.

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