scsi_debug: check for bigger value first

Even for signed types we have to check for bigger positive value first.
Otherwise it will be never happened.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Ewan Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_debug.c

@@ -4846,10 +4846,10 @@ static int __init scsi_debug_init(void)
 	/* play around with geometry, don't waste too much on track 0 */
 	sdebug_heads = 8;
 	sdebug_sectors_per = 32;
-	if (scsi_debug_dev_size_mb >= 16)
-		sdebug_heads = 32;
-	else if (scsi_debug_dev_size_mb >= 256)
+	if (scsi_debug_dev_size_mb >= 256)
 		sdebug_heads = 64;
+	else if (scsi_debug_dev_size_mb >= 16)
+		sdebug_heads = 32;
 	sdebug_cylinders_per = (unsigned long)sdebug_capacity /
 			       (sdebug_sectors_per * sdebug_heads);
 	if (sdebug_cylinders_per >= 1024) {