drm/i915: intel_unregister_dsm_handler() doesn't need struct_mutex

So don't grab the lock before calling the function.
Reviewed-by: Chris wilson <chris@chris-wilson.co.uk>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -15603,12 +15603,10 @@ void intel_modeset_cleanup(struct drm_device *dev)
 	 */
 	drm_kms_helper_poll_fini(dev);
 
-	mutex_lock(&dev->struct_mutex);
-
 	intel_unregister_dsm_handler();
 
+	mutex_lock(&dev->struct_mutex);
 	intel_fbc_disable(dev);
-
 	mutex_unlock(&dev->struct_mutex);
 
 	/* flush any delayed tasks or pending work */