fix mini playback view not reappearing when playing again after stop

(cherry picked from commit a8b1544f5d70f46d88c7ed5ed4c02eb7efd86c9a)

Sources/VLCPlayerDisplayController.m

@@ -258,7 +258,7 @@ static inline void commonSetup(VLCPlayerDisplayController *self)
             VLCMiniPlaybackView *miniPlaybackView = self.miniPlaybackView;
             if (miniPlaybackView.visible == NO) {
                 [miniPlaybackView removeFromSuperview];
-                miniPlaybackView = nil;
+                self.miniPlaybackView = nil;
             }
         };
     }