arm64: dts: qcom: sc8180x: Add a SoC-specific compatible to cpufreq-hw

Comply with bindings guidelines and get rid of errors such as:

cpufreq@18323000: compatible: 'oneOf' conditional failed, one must be fixed:
['qcom,cpufreq-hw'] is too short

Fixes: 8575f197b077 ("arm64: dts: qcom: Introduce the SC8180x platform")
Signed-off-by: Konrad Dybcio <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Signed-off-by: Viresh Kumar <[e-mail]>

arch/arm64/boot/dts/qcom/sc8180x.dtsi

···
 		};
 
 		cpufreq_hw: cpufreq@18323000 {
-			compatible = "qcom,cpufreq-hw";
+			compatible = "qcom,sc8180x-cpufreq-hw", "qcom,cpufreq-hw";
 			reg = <0 0x18323000 0 0x1400>, <0 0x18325800 0 0x1400>;
 			reg-names = "freq-domain0", "freq-domain1";