[PATCH] libata: Add ata_scsi_dev_disabled

Separate out parts of ata_scsi_find_dev to be reused in
future SAS/SATA patches.

Acked-by: Jeff Garzik <jgarzik@pobox.com>

Signed-off-by: Brian King <brking@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>