scsi: core: add scsi_io_completion_nz_result function

Break out several intertwined paths when cmd->result is non zero and place
them in the scsi_io_completion_nz_result helper function. The logic is not
changed.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>