[SCSI] Check for deleted device in scsi_device_online()

scsi_device_online() is not just a negation of SDEV_OFFLINE,
also devices in state SDEV_DEL are actually offline.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>