effects/desktopgrid: Fix config group name
The config group is formed as "Effect-" + plugin id, i.e. "desktopgrid"
Config migration from DesktopGrid to desktopgrid is already handled by a kconf_update script.
The config group is formed as "Effect-" + plugin id, i.e. "desktopgrid"
Config migration from DesktopGrid to desktopgrid is already handled by a kconf_update script.