V4L/DVB: tm6000: Partially revert some copybuf logic

Partially revert changeset 0208bef609242a2d50b95edc713a41566cae500b:

As pointed by Stefan Ringel <stefan.ringel@arcor.de>, many packets become
damaged by this change. That means that the "size" field of Video/VBI is not
presenting 180 bytes, as it should be expected.

Thanks-to: Stefan Ringel <stefan.ringel@arcor.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/staging/tm6000/tm6000-video.c

@@ -314,15 +314,15 @@ static int copy_streams(u8 *data, unsigned long len,
 				break;
 			}
 		}
-		if (cpysize < size) {
+		if (ptr + pktsize > endp) {
 			/* End of URB packet, but cmd processing is not
 			 * complete. Preserve the state for a next packet
 			 */
 			dev->isoc_ctl.pos = pos + cpysize;
 			dev->isoc_ctl.size = size - cpysize;
 			dev->isoc_ctl.cmd = cmd;
 			dev->isoc_ctl.pktsize = pktsize - (endp - ptr);
-			ptr += cpysize;
+			ptr += endp - ptr;
 		} else {
 			dev->isoc_ctl.cmd = 0;
 			ptr += pktsize;