ena: rework tx req_id validation logic

Since ena_com_tx_comp_req_id_get already checks for req_id validity,
the logic was exiting early, never giving validate_tx_req_id a chance
to trigger device reset.
Rewrite the logic so that device reset is called based on return value
of ena_com_tx_comp_req_id_get instead.

Submitted by: Artur Rojek <ar@semihalf.com>
Obtained from: Semihalf
MFC after: 2 weeks
Sponsored by: Amazon, Inc.