Let producer gain posted buffer if no released buffer exist.

ProducerQueue::Dequeue functionality does not change with the default
param gain_posted_buffer = false. It does the following otherwise:
1. try to gain a released buffer and return.
2. try to find the oldest posted buffer and return.

Bug: 80164475
Test: on Taimen with the following tests
buffer_hub-test buffer_hub_queue-test buffer_hub_queue_producer-test
dvr_api-test dvr_buffer_queue-test dvr_display-test

Change-Id: I6b27740388e53348024054396b784dbc6c08ca7e