[SYCL] Use default initializer for variables to fix Coverity warnings (#11027)

Follow up for #10913

Author: sergey-semenov

sycl/source/detail/builtins_helper.hpp

@@ -331,15 +331,15 @@ template <> struct helper<0> {
   template <typename Res, typename Op, typename T1, typename T2>
   inline void run_1v_2p(Res &r, Op op, T1 x, T2 y) {
     // TODO avoid creating a temporary variable
-    typename std::remove_pointer<T2>::type::element_type temp;
+    typename std::remove_pointer<T2>::type::element_type temp{};
     r.template swizzle<0>() = op(x.template swizzle<0>(), &temp);
     y->template swizzle<0>() = temp;
   }
 
   template <typename Res, typename Op, typename T1, typename T2, typename T3>
   inline void run_1v_2v_3p(Res &r, Op op, T1 x, T2 y, T3 z) {
     // TODO avoid creating a temporary variable
-    typename std::remove_pointer<T3>::type::element_type temp;
+    typename std::remove_pointer<T3>::type::element_type temp{};
     r.template swizzle<0>() =
         op(x.template swizzle<0>(), y.template swizzle<0>(), &temp);
     z->template swizzle<0>() = temp;