gdth: Make one abuse of scsi_cmnd less obvious

  Rather than having internal commands abuse scsi_done to call
  gdth_scsi_done, have all the places that use to call scsi_done directly
  call gdth_scsi_done, which now checks whether the command was internal,
  and calls scsi_done if not.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>