[kcmshell] Fix setting desktop entry
There's two cases we need to consider:
-
The KCM metadata is in /kservices5/kcm_foo.desktop. In this case we set the full path to this file as desktop file name
-
The KCM metadata is in /applications/kcm_foo.desktop. In this case we set 'kcm_foo' as desktop file name
This fixes showing the appropriate icon in the task manager for both cases