[SCSI] aic7xxx: avoid checking SBLKCTL register for certain cards

For cards that don't support LVD, checking the SBLKCTL register to
determine the bus singalling doesn't work.  So, check that the card
supports LVD first (AHC_ULTRA2) before checking the register.
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/aic7xxx/aic7xxx_osm.c

@@ -2539,15 +2539,23 @@ static void ahc_linux_set_iu(struct scsi_target *starget, int iu)
 static void ahc_linux_get_signalling(struct Scsi_Host *shost)
 {
 	struct ahc_softc *ahc = *(struct ahc_softc **)shost->hostdata;
-	u8 mode = ahc_inb(ahc, SBLKCTL);
+	u8 mode;
 
-	if (mode & ENAB40)
-		spi_signalling(shost) = SPI_SIGNAL_LVD;
-	else if (mode & ENAB20)
+	if (!(ahc->features & AHC_ULTRA2)) {
+		/* non-LVD chipset, may not have SBLKCTL reg */
 		spi_signalling(shost) = 
 			ahc->features & AHC_HVD ?
 			SPI_SIGNAL_HVD :
 			SPI_SIGNAL_SE;
+		return;
+	}
+
+	mode = ahc_inb(ahc, SBLKCTL);
+
+	if (mode & ENAB40)
+		spi_signalling(shost) = SPI_SIGNAL_LVD;
+	else if (mode & ENAB20)
+		spi_signalling(shost) = SPI_SIGNAL_SE;
 	else
 		spi_signalling(shost) = SPI_SIGNAL_UNKNOWN;
 }