CDROM: allow to boot from MacOS 7.6 CDROM

Reading one sector from the CDROM is always reading several (4)
from the SD card, so always set multBlock to one in this case.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>

lib/SCSI2SD/software/SCSI2SD/src/disk.c

@@ -244,7 +244,7 @@ static void doRead(uint32 lba, uint32 blocks)
 		scsiDev.phase = DATA_IN;
 		scsiDev.dataLen = 0; // No data yet
 
-		if ((blocks == 1) ||
+		if ((blocks * SDSectorsPerSCSISector(scsiDev.target->liveCfg.bytesPerSector) == 1) ||
 			unlikely(((uint64) lba) + blocks == capacity)
 			)
 		{