ASoC: dt-bindings: qcom,wcd939x: Document missing VDD_PX supply

Document VDD_PX supply on WCD9390 and WCD9395 audio codecs, which was
missed in original posting.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250526-b4-asoc-wcd9395-vdd-px-v1-5-64d3cb60313b@linaro.org


Acked-by: "Rob Herring (Arm)" <robh@kernel.org>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>