hmi-controller: don't add surface to layer in mode_random_replace()

There is no need to call layer_add_surface() in mode_random_replace()
because the surface has already been added to the layer. Rather, calling
layer_add_surface() has the issue that the child surface is displayed
below the parent surface.

Signed-off-by: Tomohito Esaki <etom@igel.co.jp>