The WSA881x shutdown GPIO is active low (SD_N), but Linux driver assumed
DTS always comes with active high.  Since Linux drivers were updated to
handle proper flag, correct the DTS.

The change is not backwards compatible with older Linux kernel.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230322193051.826167-4-krzysztof.kozlowski@linaro.org