[SYCL][NFC] Fix warning inline namespace reopened as no-inline (#1435)

Signed-off-by: Alexey Sachkov <[email protected]>

Author: AlexeySachkov

sycl/include/CL/sycl/experimental/spec_constant.hpp

@@ -20,7 +20,7 @@
 #include <CL/sycl/detail/sycl_fe_intrins.hpp>
 #include <CL/sycl/exception.hpp>
 
-namespace cl {
+__SYCL_INLINE_NAMESPACE(cl) {
 namespace sycl {
 namespace experimental {
 
@@ -56,4 +56,4 @@ template <typename T, typename ID = T> class spec_constant {
 
 } // namespace experimental
 } // namespace sycl
-} // namespace cl
+} // __SYCL_INLINE_NAMESPACE(cl)