fix warnings

src/common/knobs.h

@@ -176,7 +176,7 @@ struct starpu_perf_counter_sample_cl_values
 
 typedef void (*starpu_perf_counter_sample_updater)(struct starpu_perf_counter_sample *sample, void *context);
 
-static inline int _starpu_perf_counter_id_get_scope(const int counter_id)
+static inline enum starpu_perf_counter_scope _starpu_perf_counter_id_get_scope(const int counter_id)
 {
 	STARPU_ASSERT(counter_id >= 0);
 	return counter_id & ((1 << _STARPU_PERF_COUNTER_ID_SCOPE_BITS) - 1);