Adding staple zeroing fix

Grid/qcd/utils/WilsonLoops.h

@@ -302,7 +302,11 @@ public:
   }
 
   static void Staple(GaugeMat &staple, const std::vector<GaugeMat> &Umu, int mu) {
-    staple = Zero();
+
+    autoView(staple_v, staple, AcceleratorWrite);
+    accelerator_for(i, staple.Grid()->oSites(), Simd::Nsimd(), {
+        staple_v[i] = Zero();
+    });
 
     for (int nu = 0; nu < Nd; nu++) {