correct error message format

src/plugins/acct_gather_energy/rapl/acct_gather_energy_rapl.c

@@ -313,7 +313,7 @@ static void _get_joules_task(acct_gather_energy_t *energy)
 	double ret;
 
 	if (pkg_fd[0] < 0) {
-		error("%s: device /dev/cpu/#msr not opened "
+		error("%s: device /dev/cpu/#/msr not opened "
 		      "energy data cannot be collected.", __func__);
 		_send_drain_request();
 		return;