drm/i915: Actually attach the tv_format property to the SDVO connector

drm/i915: Actually attach the tv_format property to the SDVO connector

Attach the tv_format property to the SDVO connector instead of passing
a '0' in place of the pointer to the property. This got broken when
the SDVO connector properties were converted to atomic.

We can thank sparse for catching this:
drivers/gpu/drm/i915/intel_sdvo.c:2742:75: warning: Using plain integer as NULL pointer

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Fixes: 630d30a4ee27 ("drm/i915: Convert intel_sdvo connector properties to atomic.")
Link: http://patchwork.freedesktop.org/patch/msgid/20170615172308.10121-1-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>