Only register as the platform DELAY() implementation if the setup of the

global timer was successful, since the implementation tries to read it.

Notably, if the platform has a variable-frequency global timer (because
of dynamic frequency scaling), it doesn't set up the global timer for use
as a system timecounter, and in that case it also can't use it for DELAY.
Such platforms use different timer hardware for both timecounter and DELAY.

sys/arm/arm/mpcore_timer.c

@@ -439,7 +439,12 @@ arm_tmr_attach(device_t dev)
 	}
 
 #ifdef MULTIDELAY
-	arm_set_delay(arm_tmr_delay, sc);
+	/*
+	 * We can register as the DELAY() implementation only if we successfully
+	 * set up the global timer.
+	 */
+	if (tc_err == 0)
+		arm_set_delay(arm_tmr_delay, sc);
 #endif
 
 	return (0);