arm64: dts: qcom: sdm845-oneplus: Fix speaker GPIO node

Drop the unnecessary mux{} level to make dtbs check happy.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230407-topic-msm_dtb-v1-6-6efb4196f51f@linaro.org