net: phy: phy_led_triggers: Fix a possible null-pointer dereference in phy_led_trigger_change_speed()

In phy_led_trigger_change_speed(), there is an if statement on line 48
to check whether phy->last_triggered is NULL:
if (!phy->last_triggered)

When phy->last_triggered is NULL, it is used on line 52:
led_trigger_event(&phy->last_triggered->trigger, LED_OFF);

Thus, a possible null-pointer dereference may occur.

To fix this bug, led_trigger_event(&phy->last_triggered->trigger,
LED_OFF) is called when phy->last_triggered is not NULL.

This bug is found by a static analysis tool STCheck written by
the OSLAB group in Tsinghua University.

Signed-off-by: Jia-Ju Bai <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/phy/phy_led_triggers.c

···
 		if (!phy->last_triggered)
 			led_trigger_event(&phy->led_link_trigger->trigger,
 					  LED_FULL);
+		else
+			led_trigger_event(&phy->last_triggered->trigger, LED_OFF);
 
-		led_trigger_event(&phy->last_triggered->trigger, LED_OFF);
 		led_trigger_event(&plt->trigger, LED_FULL);
 		phy->last_triggered = plt;
 	}