Suppressed an unused variable warning for globalVertexIdx

src/core/kernels/kernels.cuh

@@ -687,6 +687,7 @@ read_out(const int idx, AcReal* __restrict__ field[], const int3 handle)
     const int3 globalVertexIdx = (int3){d_multigpu_offset.x + vertexIdx.x,                         \
                                         d_multigpu_offset.y + vertexIdx.y,                         \
                                         d_multigpu_offset.z + vertexIdx.z};                        \
+    (void)globalVertexIdx;                                                                         \
     if (vertexIdx.x >= end.x || vertexIdx.y >= end.y || vertexIdx.z >= end.z)                      \
         return;                                                                                    \
                                                                                                    \