leds: Add warning printks in error paths

Add warning printks if led_trigger_register_simple() fails.
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>

drivers/leds/led-triggers.c

@@ -183,13 +183,20 @@ int led_trigger_register(struct led_trigger *trigger)
 void led_trigger_register_simple(const char *name, struct led_trigger **tp)
 {
 	struct led_trigger *trigger;
+	int err;
 
 	trigger = kzalloc(sizeof(struct led_trigger), GFP_KERNEL);
 
 	if (trigger) {
 		trigger->name = name;
-		led_trigger_register(trigger);
-	}
+		err = led_trigger_register(trigger);
+		if (err < 0)
+			printk(KERN_WARNING "LED trigger %s failed to register"
+				" (%d)\n", name, err);
+	} else
+		printk(KERN_WARNING "LED trigger %s failed to register"
+			" (no memory)\n", name);
+
 	*tp = trigger;
 }