accel/habanalabs: call to HW/FW err returns 0 when no events exist

This commit modifies the call to retrieve HW or FW error events to
return success when no events are pending, as done in the calls to
other events.

Signed-off-by: Moti Haimovski <mhaimovski@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>