When driver unload is triggered, check_for_leaks complains,
saying it finds pending entries in TxLookupQueue of ENDPOINT_0.
Flush pending entries in TxLookupQueue for ENDPOINT_0 during htc_cleanup.
Change-Id: Ica661453d5cef283526cfa1e7267d5349b5e2310
CRs-Fixed: 2249980