drm/i915: re-add locking around hw state readout

To silence locking complaints.  This was a rebase failure on my part in

commit fa9fa083d0606cb323f6105c17702460ea0a6780
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Tue Feb 11 15:28:56 2014 -0800

    drm/i915: read out hw state earlier v2

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -11042,7 +11042,9 @@ void intel_modeset_init(struct drm_device *dev)
 	/* Just in case the BIOS is doing something questionable. */
 	intel_disable_fbc(dev);
 
+	mutex_lock(&dev->mode_config.mutex);
 	intel_modeset_setup_hw_state(dev, false);
+	mutex_unlock(&dev->mode_config.mutex);
 }
 
 static void