libata-sff: update bmdma host bus error handling

libata-sff: update bmdma host bus error handling

* Clearing IRQ from ata_sff_error_handler() is necessary only when the
  port is gonna be thawed before performing EH actions and some
  controllers don't like being accessed after certain failure modes
  until they're reset.  Clear IRQ iff the port is being thawed.

* When the controller succesfully indicated bus error, the point of
  thawing doesn't matter.  Move thawing inside bmdma part of EH.  This
  is a bit ugly but will ease code reorganization later.

* Remove the unneeded ata_sff_sync().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>