Fix bad cast, which truncates free storage value.

src/Camera/QGCCameraControl.cc

@@ -245,7 +245,7 @@ QGCCameraControl::photoStatus()
 QString
 QGCCameraControl::storageFreeStr()
 {
-    return QGCMapEngine::bigSizeToString(static_cast<quint64>(_storageFree * 1024 * 1024));
+    return QGCMapEngine::bigSizeToString(static_cast<quint64>(_storageFree) * 1024 * 1024);
 }
 
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