Fix endless loop in SCSI SPI transport class

If the driver doesn't update the peroid, we go
around forever.  The fix is to keep our old period
unless the driver returns a greater one.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/scsi_transport_spi.c

@@ -394,6 +394,7 @@ spi_dv_retrain(struct scsi_request *sreq, u8 *buffer, u8 *ptr,
 
 
 	for (;;) {
+		int newperiod;
 		if (compare_fn(sreq, buffer, ptr, DV_LOOPS))
 			/* Successful DV */
 			break;
@@ -401,7 +402,8 @@ spi_dv_retrain(struct scsi_request *sreq, u8 *buffer, u8 *ptr,
 		/* OK, retrain, fallback */
 		if (i->f->get_period)
 			i->f->get_period(sdev);
-		period = spi_period(sdev);
+		newperiod = spi_period(sdev);
+		period = newperiod > period ? newperiod : period;
 		if (period < 0x0d)
 			period++;
 		else