libata: only call ->done once all per-tag ressources are released

When calling ->done before releasing resources we could run into a
race where the SCSI midlayer sends another command and races with
the resources beeing manipulated.  For libata this can't currently
happen as synchronization happens at a higher level, but I'd still
like to fix it to future proof libata and to avoid copy & paste
into SCSI drivers where this pattern has led to reproducible crashes.

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