scsi: scsi_dh: Return SCSI_DH_XX error code from ->attach()

Rather than having each device handler implementing their own error
mapping, have the ->attach() call return a SCSI_DH_XXX error code and
implement the mapping in scsi_dh_handler_attach().

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>