[media] cx88: added support for Leadtek WinFast DTV1800 H with XC4000 tuner

This patch implements support for the Leadtek WinFast DTV1800 H card with
XC4000 tuner (107d:6f38).

Signed-off-by: Istvan Varga <istvan_v@mailbox.hu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>