arm64: dts: meson-gx: fix mhu compatible

This fixes the following DT schemas check errors:
meson-gxbb-nanopi-k2.dt.yaml: mailbox@404: compatible:0: 'amlogic,meson-gx-mhu' is not one of ['amlogic,meson-gxbb-mhu']
meson-gxl-s805x-libretech-ac.dt.yaml: mailbox@404: compatible:0: 'amlogic,meson-gx-mhu' is not one of ['amlogic,meson-gxbb-mhu']
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm64/boot/dts/amlogic/meson-gx.dtsi

@@ -490,7 +490,7 @@ sysctrl: system-controller@0 {
 			};
 
 			mailbox: mailbox@404 {
-				compatible = "amlogic,meson-gx-mhu", "amlogic,meson-gxbb-mhu";
+				compatible = "amlogic,meson-gxbb-mhu";
 				reg = <0 0x404 0 0x4c>;
 				interrupts = <GIC_SPI 208 IRQ_TYPE_EDGE_RISING>,
 					     <GIC_SPI 209 IRQ_TYPE_EDGE_RISING>,