leds: class: If no default trigger is given, make hw_control trigger the default trigger

If a hw_control_trigger is defined, it's usually desirable to make it
the default trigger. Therefore make it the default trigger, except
the driver explicitly set a default trigger.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/f33543de-3800-488f-a779-1fa282614462@gmail.com


Signed-off-by: Lee Jones <lee@kernel.org>