Update simd warp example

[pkestene]

A tentative fix for this example.

the type simd::simd<double,simd::simd_abi::cuda_warp<32>>, used in the old example, disappeared, so replaced by simd_t = Kokkos::Experimental::native_simd<double> which width/ simd size is 1 when exec space is Cuda (scalar type).