[PATCH] don't set underflow for REQ_BLOCK_PC

I got underflow warnings and failures when sending an INQUIRY page 0x83
via the SG_IO REQ_BLOCK_PC interface.

The underflow field should only be set if we know for certain the size of
the data being transfered, so fix this by leaving it at zero for scsi
REQ_BLOCK_PC cases.

drivers/scsi/sd.c

@@ -174,7 +174,6 @@ static int sd_init_command(struct scsi_cmnd * SCpnt)
 			timeout = rq->timeout;
 
 		SCpnt->transfersize = rq->data_len;
-		SCpnt->underflow = rq->data_len;
 		goto queue;
 	}
 

drivers/scsi/sr.c

@@ -301,7 +301,6 @@ static int sr_init_command(struct scsi_cmnd * SCpnt)
 			timeout = rq->timeout;
 
 		SCpnt->transfersize = rq->data_len;
-		SCpnt->underflow = rq->data_len;
 		goto queue;
 	}