drm/i915: VLV doesn't have SDVO

Don't call intel_sdvo_init() for VLV.

Preserve the same behaviour as when intel_sdvo_init() would
have returned false.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>