arm64: dts: allwinner: h6: Fix PMU compatible

The commit 7aa9b9e ("arm64: dts: allwinner: H6: Add PMU mode")
introduced support for the PMU found on the Allwinner H6. However, the
binding only allows for a single compatible, while the patch was adding
two.

Make sure we follow the binding.

Fixes: 7aa9b9e ("arm64: dts: allwinner: H6: Add PMU mode")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>

arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi

@@ -70,8 +70,7 @@
 	};
 
 	pmu {
-		compatible = "arm,cortex-a53-pmu",
-			     "arm,armv8-pmuv3";
+		compatible = "arm,cortex-a53-pmu";
 		interrupts = <GIC_SPI 140 IRQ_TYPE_LEVEL_HIGH>,
 			     <GIC_SPI 141 IRQ_TYPE_LEVEL_HIGH>,
 			     <GIC_SPI 142 IRQ_TYPE_LEVEL_HIGH>,