scsi-disk.c: Fix compilation with -DDEBUG_SCSI

In scsi-disk.c, if you #define DEBUG_SCSI=1, you get:
hw/scsi/scsi-disk.c: In function 'scsi_disk_emulate_command':
hw/scsi/scsi-disk.c:2018: error: 'SCSIRequest' has no member named 'buf'

Change the debugging statement to match the actual value tested.
Signed-off-by: NPaul Janzen <pcj@pauljanzen.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/scsi/scsi-disk.c

@@ -2015,7 +2015,7 @@ static int32_t scsi_disk_emulate_command(SCSIRequest *req, uint8_t *buf)
     case VERIFY_10:
     case VERIFY_12:
     case VERIFY_16:
-        DPRINTF("Verify (bytchk %lu)\n", (r->req.buf[1] >> 1) & 3);
+        DPRINTF("Verify (bytchk %d)\n", (req->cmd.buf[1] >> 1) & 3);
         if (req->cmd.buf[1] & 6) {
             goto illegal_request;
         }