Camera: fix per stream error code for HAL buffer manager

Also some refactoring to make the code more readable and less
indent.
Also clarify the unknown error case that per stream error code
might still be provided.

Test: GCA smoke test and camera CTS
Bug: 120986771
Change-Id: I3b7d3eadfe3895a3fdf3888735a3932d5c6c03bc