staging: ft1000: Fix kernel panic when use ioctl.

During ioctl testing was observed kernel panic beuase
file->private_data pointer was not correctly set when
debugfs file was created. Add correct pointer setup.

Signed-off-by: Marek Belisko <marek.belisko@open-nandra.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>