vcl: fix typo in the Android stub of sgvspln

The intention is to call the real function, not the stub itself.

Change-Id: I4bfd3020871c68951b19a3c63ea9a2dc4d736be7

vcl/source/filter/sgvspln.cxx

@@ -29,7 +29,7 @@ namespace std
 template<typename T>
 T copysign(T x, T y)
 {
-    return copysign(x, y);
+    return ::copysign(x, y);
 }
 }
 #endif