visca: Fix power state not getting updated

The visca driver wasn't querying the camera when the power state
changed. This resulted in not being able to turn the camera back on
after turning it off. Fix this by adding "power_on" to the stale
properties list when changing the power state.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

src/ptz-visca.cpp

@@ -251,7 +251,8 @@ const PTZInq
 				      {new int_field("color_hue", 2, 0b1111)});
 
 const PTZCmd VISCA_CommandCancel("8120ff", {new visca_u4("socket", 1)});
-const PTZCmd VISCA_CAM_Power("8101040000ff", {new visca_flag("power_on", 4)});
+const PTZCmd VISCA_CAM_Power("8101040000ff", {new visca_flag("power_on", 4)},
+			     "power_on");
 const PTZInq VISCA_CAM_PowerInq("81090400ff", {new visca_flag("power_on", 2)});
 
 const PTZCmd VISCA_CAM_Zoom_Stop("8101040700ff", "zoom_pos");