leds: syscon: Support 'reg' in addition to 'offset' for register address

The register-bit-led binding now also supports 'reg' in addition to
'offset' for the register address. Add support to the driver to get the
address from 'reg'.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20231025190619.881090-2-robh@kernel.org


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