libata: fix locking for sas paths

For historical reasons, libsas uses the scsi host lock as the ata port
lock, and libata always uses the ata host.  For the old eh, this was
largely irrelevant since the two locks were never mixed inside the
code.  However, the new eh has a case where it nests acquisition of
the host lock inside the port lock (this does look rather deadlock
prone).  Obviously this would be an instant deadlock if the port lock
were the host lock, so switch the libsas paths to use the ata host
lock as well.

Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>