[media] v4l2-ctrls: queryctrl shouldn't attempt to replace V4L2_CID_PRIVATE_BASE IDs

When queryctrl is called with a V4L2_CID_PRIVATE_BASE control ID, then
currently it is replaced by the real internal ID. This is not according to
the spec so keep the V4L2_CID_PRIVATE_BASE ID in this case.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>