drm/i915: Pass dev_priv to intel_is_dual_link_lvds()

Make things look a bit nicer by passing dev_priv to
intel_is_dual_link_lvds().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190318202653.15217-3-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>