drm/meson: venc_cvbs: no more return -ENODEV if CVBS is not available

Since this is managed now by the components code, if CVBS is not available
and HDMI neither, the drm driver won't bind anyway.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>