Skyfan DC fan: make speed and preset optional

Issue #1959

custom_components/tuya_local/devices/skyfan_dc_fan.yaml

@@ -11,6 +11,7 @@ primary_entity:
     - id: 2
       type: string
       name: preset_mode
+      optional: true
       mapping:
         - dps_val: smart
           value: smart
@@ -21,6 +22,7 @@ primary_entity:
     - id: 3
       type: integer
       name: speed
+      optional: true
       range:
         min: 1
         max: 5