staging/android: remove len field from struct sync_fence_info

After removing driver_data struct sync_fence_info has now a fixed size,
thus it doesn't need any field to tell its size, it is already known.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>