[media] cx23885: Don't use memset on vidioc_ callbacks

vidioc_g_tuner should not do any memset for the parameters. Core
already does that. In particular, V4L2 core now does some handling
for the tuner type, and the tuner-core module relies on that.

So, doing any memset there is a very bad idea.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>