Revert "[SCSI] Remove full sg table memset()"

A bit too eager - we definitely need to clear the sg table
initially, so that we don't accidentally have ->page & 0x01
true and think that is a chain pointer.

This reverts commit f5c0dde4c6.

drivers/scsi/scsi_lib.c

@@ -764,6 +764,8 @@ struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
 		if (unlikely(!sgl))
 			goto enomem;
 
+		memset(sgl, 0, sizeof(*sgl) * sgp->size);
+
 		/*
 		 * first loop through, set initial index and return value
 		 */