tests: minor fixes following icc's warnings

tests/datawizard/readers_and_writers.c

@@ -73,7 +73,7 @@ int main(int argc, char **argv)
 		else
 			task->cl = &r_cl;
 
-		int ret = starpu_task_submit(task);
+		ret = starpu_task_submit(task);
 		if (ret == -ENODEV) goto enodev;
 		STARPU_CHECK_RETURN_VALUE(ret, "starpu_task_submit");
 	}

tests/main/multithreaded_init.c

@@ -22,9 +22,10 @@
 
 #define NUM_THREADS 5
 
-void *launch_starpu(void *id)
+void *launch_starpu(void *unused)
 {
 	int ret;
+	(void) unused;
 	ret = starpu_init(NULL);
 	if (ret == -ENODEV)
 		exit(STARPU_TEST_SKIPPED);