fix type error

(cherry picked from commit 110cc19183db35b168231b69d1681dd9323eadf0)
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

Sources/VLCMovieViewController.m

@@ -1537,7 +1537,7 @@ currentMediaHasTrackToChooseFrom:(BOOL)currentMediaHasTrackToChooseFrom
     if (notification)
         self.brightnessSlider.value = [(UIScreen *)notification.object brightness] * 2.;
     else if (![[UIDevice currentDevice] hasExternalDisplay])
-        self.brightnessSlider.value = [[[UIScreen screens] firstObject] brightness] * 2.;
+        self.brightnessSlider.value = [(UIScreen *)[[UIScreen screens] firstObject] brightness] * 2.;
 }
 
 #pragma mark - playback view