staging: dgrp: info leak in dgrp_dpa_ioctl()

If "nd->nd_vpd_len" is less than 512 then the last part of the
"vpd.vpd_data" has uninitialized stack information.  We need to clear it
before copying the buffer to user space.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>