[SYCL] Fix sporadic auto_flush lit tests fail (#1195)

Signed-off-by: Igor Dubinov <igor.dubinov@intel.com>

Author: idubinov

sycl/source/detail/stream_impl.cpp

@@ -41,6 +41,7 @@ void stream_impl::flush() {
       range<1>(BufferSize_), id<1>(OffsetSize));
 
   printf("%s", HostAcc.get_pointer());
+  fflush(stdout);
 }
 } // namespace detail
 } // namespace sycl