drm/i915: MCH_SSKPD is a 64 bit register on Haswell

And the SNB_READ_WM0_LATENCY macro is not valid anymore because we
have the "New WM0" at 63:56, so the "Old WM0" could maybe be zero if
the new one is not zero.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -4633,7 +4633,7 @@ void intel_init_pm(struct drm_device *dev)
 			}
 			dev_priv->display.init_clock_gating = ivybridge_init_clock_gating;
 		} else if (IS_HASWELL(dev)) {
-			if (SNB_READ_WM0_LATENCY()) {
+			if (I915_READ64(MCH_SSKPD)) {
 				dev_priv->display.update_wm = haswell_update_wm;
 				dev_priv->display.update_sprite_wm = sandybridge_update_sprite_wm;
 			} else {