drm/i915: Fix GMBUSFREQ on vlv/chv

vlv_cdclk_freq is in kHz but we need MHz for the GMBUSFREQ divider.

This is a regression from:
commit f8bf63fdcb1f82459dae7a3f22ee5ce92f3ea727
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Fri Jun 13 13:37:54 2014 +0300

    drm/i915: Kill duplicated cdclk readout code from i2c

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -4585,7 +4585,7 @@ static void vlv_update_cdclk(struct drm_device *dev)
 	 * BSpec erroneously claims we should aim for 4MHz, but
 	 * in fact 1MHz is the correct frequency.
 	 */
-	I915_WRITE(GMBUSFREQ_VLV, dev_priv->vlv_cdclk_freq);
+	I915_WRITE(GMBUSFREQ_VLV, DIV_ROUND_UP(dev_priv->vlv_cdclk_freq, 1000));
 }
 
 /* Adjust CDclk dividers to allow high res or save power if possible */