e_comp_wl_data: set visible value of the drag_client to False when the drag finished.

e_comp_wl_data: set visible value of the drag_client to False when the drag finished.

Set visible value of the drag client to 0 when the drop finished.

There're many log about show blocked of the drag client after the drop
finished.
It's caused by the visible value of the drag client is 1 even though the
drag client didn't draw their surface after the drop finished.
To solve this problem, we set the visible value of the drag client to 0
when the drop finished.

Change-Id: I6994de1e5f11a3d1e1d2922948f43f10fd8d1753