Fix variance calculation

src/targets/gpu/kernels/include/migraphx/kernels/layernorm.hpp

@@ -57,12 +57,13 @@ __device__ void generic_binary_layernorm(
 
         auto mean_x  = means[0];
         auto mean_x2 = means[1];
+        auto variance = mean_x2 - (mean_x * mean_x);
 
         r.inner([&](auto& y, auto x1, auto x2, auto... xs) {
             auto x = op(x1, x2);
             auto m = x - mean_x;
             // m * rsqrt(mean(m ^ 2) + 1e-12)
-            y = compute(m * rsqrt(mean_x2 - mean_x + value_type{1e-12}), xs...);
+            y = compute(m * rsqrt(variance + value_type{1e-12}), xs...);
         })(output, input1, input2, inputs...);
     });
 }