dt-bindings: leds: qcom-lpg: Document PM8550 compatible

The PM8550 PWM modules are compatible with the PM8350c PWM modules,
document the PM8350c PWM compatible as fallback for the PM8550 PWM.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230522-topic-sm8550-upstream-pm8550-lpg-v2-1-c5117f1d41f9@linaro.org


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