fix typo

doc/vector_scal_c.texi

@@ -15,7 +15,7 @@ extern void scal_cuda_func(void *buffers[], void *_args);
 extern void scal_opencl_func(void *buffers[], void *_args);
 
 static starpu_codelet cl = @{
-    .where = STARPU_CPU | STARPU_CUDA | STARPU_USE_OPENCL,
+    .where = STARPU_CPU | STARPU_CUDA | STARPU_OPENCL,
     /* CPU implementation of the codelet */
     .cpu_func = scal_cpu_func,
 #ifdef STARPU_USE_CUDA