drm/i915: restore fixed FDI link rate on Sandybridge

FDI_PLL_BIOS_0 register is for Ironlake only, don't apply to
Sandybridge.
Original-patch-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -345,8 +345,11 @@ intel_find_pll_ironlake_dp(const intel_limit_t *, struct drm_crtc *crtc,
 static inline u32 /* units of 100MHz */
 intel_fdi_link_freq(struct drm_device *dev)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	return (I915_READ(FDI_PLL_BIOS_0) & FDI_PLL_FB_CLOCK_MASK) + 2;
+	if (IS_GEN5(dev)) {
+		struct drm_i915_private *dev_priv = dev->dev_private;
+		return (I915_READ(FDI_PLL_BIOS_0) & FDI_PLL_FB_CLOCK_MASK) + 2;
+	} else
+		return 27;
 }
 
 static const intel_limit_t intel_limits_i8xx_dvo = {