Minor change: rely rather on Eigen to compute addition in Faust::Vect += operator.

Eigen might be more efficient to do it at low-level.
This commit is next to the previous one (e2c514be).

src/faust_linear_operator/CPU/faust_Vect.hpp

@@ -184,10 +184,7 @@ void Faust::Vect<FPP,Cpu>::operator+=(const Faust::Vect<FPP,Cpu>& v)
 
 	  handleError(m_className,"operator+= : dimensions are in conflict");
    }
-   FPP* ptr_data = getData();
-   const FPP* v_ptr_data = v.getData();
-   for (int i=0 ; i<size() ; i++)
-      ptr_data[i] += v_ptr_data[i];
+   vec += v.vec;
 }