leds: triggers: default-on: Add module alias for module auto-loading

A bigger number of board device tree files, plus few drivers, set
default-on as default trigger for LED's. Therefore add an alias for
module auto-loading.

Signed-off-by: Heiner Kallweit <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/trigger/ledtrig-default-on.c

···
 MODULE_AUTHOR("Nick Forbes <[e-mail]>");
 MODULE_DESCRIPTION("Default-ON LED trigger");
 MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("ledtrig:default-on");