arm64: dts: meson-g12b-ugoos-am6: fix board compatible

Add missing amlogic,s922x in the board compatible list.

It fixes:
meson-g12b-ugoos-am6.dt.yaml: /: compatible: ['ugoos,am6', 'amlogic,g12b'] is not valid under any of the given schemas
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200326165958.19274-4-narmstrong@baylibre.com

arch/arm64/boot/dts/amlogic/meson-g12b-ugoos-am6.dts

@@ -14,7 +14,7 @@
 #include <dt-bindings/sound/meson-g12a-tohdmitx.h>
 
 / {
-	compatible = "ugoos,am6", "amlogic,g12b";
+	compatible = "ugoos,am6", "amlogic,s922x", "amlogic,g12b";
 	model = "Ugoos AM6";
 
 	aliases {