USB: chaoskey read offset bug

Rng reads in chaoskey driver could return the same data under
the certain conditions.

Signed-off-by: Alexander Inyukhin <shurick@sectorb.msk.ru>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/chaoskey.c

@@ -472,7 +472,7 @@ static int chaoskey_rng_read(struct hwrng *rng, void *data,
 	if (this_time > max)
 		this_time = max;
 
-	memcpy(data, dev->buf, this_time);
+	memcpy(data, dev->buf + dev->used, this_time);
 
 	dev->used += this_time;