YX316 aroma diffuser: default sound switch to off

Avoid the sound switch showing as disabled when it is not reported by the device.

Issue #1134

custom_components/tuya_local/devices/yx316wifi_aroma_diffuser.yaml

@@ -100,3 +100,7 @@ secondary_entities:
             icon: "mdi:speaker"
           - dps_val: false
             icon: "mdi:speaker-off"
+          - dps_val: null
+            icon: "mdi:speaker-off"
+            value: false
+            hidden: true