libata: relocate sdev->manage_start_stop configuration

After 9b8e8de7, manage_start_stop configuration depends on valid ATA
device.  Move it into ata_scsi_dev_config().  This was detected by the
coverity checker.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>