[SCSI] tmscsim: Further clean-up of the driver

 - The saved sg_count was a leftover from the time the driver was doing
   dma mapping by himself. But now that scsi-ml is called for the mapping
   it is not the drivers responsibility.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Acked-by: G. Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>