libata: call ->scsi_done from ata_scsi_simulate

We always need to call ->scsi_done after we've finished emulating a
command, so do it in a single place at the end of ata_scsi_simulate.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tejun Heo <tj@kernel.org>