ARM: dts: BCM53573: Don't use nonexistent "default-off" LED trigger

Such a trigger doesn't exist in Linux and is not needed as LED is being
turned off by default. This could cause errors in LEDs core code when
trying to set default trigger.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>