inhibit/dbus: fix service and path

According to https://web.archive.org/web/20080828095706/https://people.freedesktop.org/~hughsient/temp/power-management-spec-0.2.html the correct service name does not include `.Inhibit` and the path includes `/Inhibit`.

This essentially reverts beec9e78


(cherry picked from commit 77a2d21b)