dt-bindings: leds: Fix reference to definition of default-state

At least since the YAML conversion, the default-state property is
described in leds/common.yaml, so there's no need to point to another
file for its definition.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230814163116.1696092-1-j.neuschaefer@gmx.net


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