drm/i915: intel_prepare_ddi_buffers should be static

It's not even declared on header files.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -84,7 +84,8 @@ static enum port intel_ddi_get_encoder_port(struct intel_encoder *intel_encoder)
  * in either FDI or DP modes only, as HDMI connections will work with both
  * of those
  */
-void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port, bool use_fdi_mode)
+static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port,
+				      bool use_fdi_mode)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 reg;