[media] cx231xx: replace ioctl by unlocked_ioctl

There was already a core lock, so why wasn't ioctl already replaced by
unlock_ioctl?
This patch switches to unlocked_ioctl.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>