scsi: core: scsi_io_completion: comment on end_request return

scsi_end_request() is called multiple times from scsi_io_completion() which
branches on its bool returned value. Add comment before the static
definition of scsi_end_request() about the meaning of that return.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>