SIMD: suppress a uninitialized variable warning (kokkos#6294)

* Added an extra branch in attempt to fix a spurious uninitialized variable warning

* Apply review feedback on simd/unit_tests/TestSIMD.cpp

Co-authored-by: Damien L-G <dalg24+github@gmail.com>

---------

Co-authored-by: Damien L-G <dalg24+github@gmail.com>

simd/unit_tests/TestSIMD.cpp

@@ -192,8 +192,11 @@ void host_check_math_op_one_loader(UnaryOp unary_op, std::size_t n,
     bool const loaded_arg = loader.host_load(args + i, nlanes, arg);
     if (!loaded_arg) continue;
     simd_type expected_result;
-    for (std::size_t lane = 0; lane < nlanes; ++lane) {
-      expected_result[lane] = unary_op.on_host_serial(T(arg[lane]));
+    // gcc 8.4.0 warns if using nlanes as upper bound about arg
+    // being uninitialized
+    for (std::size_t lane = 0; lane < simd_type::size(); ++lane) {
+      if (lane < nlanes)
+        expected_result[lane] = unary_op.on_host_serial(T(arg[lane]));
     }
     simd_type const computed_result = unary_op.on_host(arg);
     host_check_equality(expected_result, computed_result, nlanes);