HDMI sync light: use white instead of brightness for color mode

In HA, brightness is reserved for lights that only support brightness.
Lights that support color and white with brightness control but no
color temperature, need to use white rather than brightness.

Issue #1788

custom_components/tuya_local/devices/hdmi_sync_light.yaml

@@ -15,7 +15,7 @@ primary_entity:
       name: color_mode
       mapping:
         - dps_val: white
-          value: brightness
+          value: white
         - dps_val: colour
           value: hs
       optional: true