[SCSI] Redundant memset in scsi_alloc_sgtable

scsi_init_io calls scsi_alloc_sgtable and then calls blk_rq_map_sg
to initialize the scatterlist structure.  blk_rq_map_sg() already
memset the structure for every new segment.  That makes the memset
in scsi_alloc_sgtable unnecessary.

Patch to delete the extra memset in scsi_alloc_sgtable.  Tested on
a x86_64 machine.  Looks stable to me.
Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/scsi_lib.c

@@ -614,8 +614,6 @@ static struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, int gfp_mas
 
 	sgp = scsi_sg_pools + cmd->sglist_len;
 	sgl = mempool_alloc(sgp->pool, gfp_mask);
-	if (sgl)
-		memset(sgl, 0, sgp->size);
 	return sgl;
 }