Lytmi HDMI sync: rename v component so brightness is preferred

Since the light only supports color mode, brightness is
always sent as the hsv dp, but that interferes with scene selection.
Since the light has a brightness dp, it is obviously supposed to be used,
even thought the light does not support white mode, contrary to the way
other Tuya lights work.

Based on PR #3082

custom_components/tuya_local/devices/lytmi_hdmisync_backlight.yaml

@@ -29,7 +29,7 @@ entities:
             range:
               min: 0
               max: 1000
-          - name: v
+          - name: w
             bytes: 2
             range:
               min: 0