backlight: lm3639: Fully initialize backlight_properties during probe

[ Upstream commit abb5a5d951fbea3feb5c4ba179b89bb96a1d3462 ]

props is stack allocated and the fields that are not explcitly set
by the probe function need to be zeroed or we'll get undefined behaviour
(especially so power/blank states)!

Fixes: 0f59858d ("backlight: add new lm3639 backlight driver")
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20240220153532.76613-3-daniel.thompson@linaro.org


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