staging: kpc2000: Fix a stack information leak in kp2000_cdev_ioctl()

The kp2000_regs struct has a 4 byte hole between ->hw_rev and ->ssid so
this could leak stack information to the user.  This patch just memsets
the whole struct to zero.

Fixes: 7dc7967f ("staging: kpc2000: add initial set of Daktronics drivers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>